Tinkerings of a sculptor and metalsmith...

Using Photopolymers

2011-12-30T20:36:00.000Z

I have been using both Imagon-HD photopolymer film, and photopolymer plates. The latter has been the easier to use and more reliable, but the former more fun. Both need exposing to UV light (I only have a black-light UV tube) through a line-art transparency, although in fact for the film I use images printed onto tracing paper. This is partly because the swanky do-it-all office photocopiers will no longer accept any old material to print on without your losing your insurance and maintenance contracts (and job probably). But my ancient printer works perfectly on tracing paper with no loss of quality in the exposed result.
The three images on the left all use Imagon-HD film, which is a pre-sensitised gelatine product, glued onto metal stock with water and subsequently dried. The first is nickel silver subsequently etched in dilute nitric acid with text; the second shows nickel silver on top etched with a Greek key design, the bottom is a piece of copper still bearing the exposed and developed film; the third is a longer strip of nickel silver with exposed and developed film (but not yet etched).The Fourth shows a piece of hammered brass on top, and a sintered fine silver pendent made from a photopolymer plate mold. This plate material, again a presensitised gelatine product (with an offensive and possibly somewhat toxic smell), after exposure to UV light hardens in such a way that it does not wash out in warm water. The parts not so exposed do however wash out. The result is a 3-D mold or stamp, which I used to form the sintered silver paste. After drying, this was fired in the usual way for such materials, then enamelled with aqua enamel at about 850°C.The fifth picture shows the same fine silver pendent before enamelling, along with two examples of etching done by students in my jewellery class using resist paint on nickel silver; and some sintered silver fired pieces formed from commercial molds.

Tapered tube & Wire

2011-08-10T10:43:00.003+01:00

I have never had any particular interest in tapered wire or tube until now, when I was shown some bangles and ear-rings, and realised I didn't know how they were made. I recently posted a query on Orchid / Ganoksin, and am currently waiting for information from more experienced metalsmiths. The picture above left shows a solid silver-plated copper hoop, tapered smoothly in both directions, two solid tapered nickel silver finger rings, and a hollow 0.5mm-thick sterling ear hoop. The picture on the right shows the ear hoop sawn in half, it can plainly be seen to have seams around the interior and exterior periphery. However I have also been shown one that has only an interior seam. Anyone give me some ideas of how these are made? By way of experiment, I hammered a 30x10mm cylindrical sprue of pewter into a double-ended spindle shape reminiscent of some of the crescent designs above, although I've not yet worked out how to hammer or press it into a crescent without damaging the cross section.

Making a hollow cage

2011-05-23T14:54:00.006+01:00

After seeing a very nice hinged ball containing a natural pearl, I thought I would try it. It was easy making a hemispherical ball from rolled copper wire; 1.6mm copper wire was rolled to 1.8x1.0mm. Three lengths of 30mm were sawn from this. Two were given a 45° chamfer at each end then soldered at one end.

The trident was then shaped round a 16mm dome and domed in a 19mm dome. This was repeated with a second set of three strips to give two half-cages. Each soldered triplet was soldered at the other end then again domed, but in a 20mm dome with an 18mm punch. The cages looked very attractive, but the hard part is to try to find a way to hinge them neatly. I subsequently soldered a small copper rectangle, about 4x5x1mm, to one end of one triplet. This however proved not thick enough for drilling for a hinge.

More etching

2011-01-26T16:34:00.002Z

By way of student demos, I rolled then etched the 2p bronze coin as shown sometime in the summer of 2010. This coin was one of my stash of pre-1992 coins which were entirely made of copper alloy; after that date, they are made of steel with a copper plated surface, and not so easy or safe in the rolling mill. After etching, I 'enamelled' it with coloured polyester resin. Although there are many adherents of using various acid and peroxide mixes for etching of copper, I find that ferric chloride solution (with or without the addition of citric acid) has fewer problems. In particular, no nasty fumes, and much less deterioration of the resist (which in my case is usually tinted shellac in alcohol).

Testing for nickel

2010-12-13T16:34:00.004Z

The standard qualitative test for nickel is to use a solution of DMG (dimethylglyoxime). I followed the instructions in Hoke for making 20ml solution of DMG (dimethylglyoxime) in distilled water, boiling it for some time. However it deposited a bunch of crystals, and on checking online I find that it is ‘virtually insoluble’ in cold water; Merck for example says solubility is 0.6g/l. I find it inexplicable that Hoke should seem to be inaccurate on this matter. The supernatant liquid reacted with some strong nickel chloride (plating solution) to give a very faint pink precipitate. Things were (literally) much rosier when I added methylated spirits to the residue DMG crystals as well as water, to get a much stronger solution. This precipitated a heavy deposit of beetroot-red organometallic complex (see picture left), with, strangely, no trace of colouration in the supernatant liquid of the methylated spirits dye, which seemed to have 'complexed out' of it at the same time. Apparently the DMG solution needs to be not too acidic in pH for the test to work; better for it to be slightly alkaline. In more strongly acid solution, the same reagent is apparently a useful test for palladium, with which it gives a canary-yellow precipitate (which I have not tested). More information can be found from people who test meteorites; who variously suggest that the DMG should be dissolved in methanol at 10gm/litre, and that the results can be masked by many other metallic ions, especially cobalt.

Silversmithing at London Met

2010-09-08T14:18:00.007+01:00

I signed up for ten 1-day sessions of silversmithing at Sir John Cass Faculty of Art, Media and Design, a school within London Metropolitan University. The sessions were tutored by Steve Wager, and financed for me by London Central YMCA as part of my continuing professional development. Sign of the times; I signed up together with only two others, both young women in their twenties. Also on the course were more than a dozen 'old timers' fairly evenly split between the sexes and mostly over fifty years old (but still mostly younger than me!). For full course notes, see my Wordpress blog at this link (opens in new window)

I found my time there hugely enjoyable, and 'bashed out' my first bowl from 1mm gilding metal (first & last stages shown above), followed by a spoon in copper,

then a pill-pot in gilding metal;

I also made a start on a larger bowl, and independently hammered a scrap silver sprue into a small spoon. I'm planning to take the Autumn term starting in early October.

Discriminating between diamond and CZ

2010-01-20T15:36:00.003Z

After a tip from Orchid, I placed a 2.5mm CZ and a 2.5mm diamond face-down on a sheet of white paper which had had fine alternating-colour lines drawn along it. On careful inspection with a loupe, it was apparent that one couldn’t see the coloured lines through the diamond, but they were fairly visible, though distorted, seen through the CZ (see picture in the right side-bar). The implication, in addition to giving a test for discriminating between the two materials, is that light passes from the back to the front, then gets reflected from the lined paper, before passing again to the back and out to the eye. One wonders what difference there might be if both stones were laid face-down on a light box. I also tried adding a fine-silver backing to a CZ, mindful of the beauty of Swarovski crystal. The result was very disappointing; the translucent quality of the CZ was replaced by a sense of rather dirty grey in some of the darker areas, though the general amount of light reflected didn't seem affected. I'm pretty sure there's a good reason why no-one sells foil-backed CZ...

Some ins-and-outs of twisting sterling square rod

2009-12-08T20:20:00.001Z

In pursuit of making a twisted square-section sterling ring, some old square rod of about 2mm side was annealed then twisted with one end held in a vice, the other in pliers. This gave a twist of about 2.2mm diameter, with about 18 twists in a length of 76mm. The first picture below shows the original square rod, and the twist result. I subsequently found that it was much more convenient to grip with rod at the operator end with bulldog grips, resulting in an easier, more even and denser twist.

This twist was then annealed and formed into an open (unsoldered) ring before polishing, as in the second picture above. The result, although reasonably pleasant after polishing with radial polishing wheels, was aesthetically too coarse a gauge. It was then re-annealed, straightened then untwisted. To my surprise, I managed to then roll it through the mill wire rollers to re-form perfect 2mm square rod. These latter wire rollers were not actually much use, because their minimum gauge is in fact 2mm – this accounts for the prevalence of 2mm square rod in my scrap box (all produced from old sprues). So it was rolled through the flat rollers instead, rotating the rod a quarter revolution each pass, to give a final gauge of 1.8mm square. It was then twisted in two stages with annealing to give a diameter of 1.85mm with 46 twists per 76mm.
The third picture above shows the very sharp profile of the spiral twist made by the above process, which naturally would be expected to be uncomfortable if made into a ring. So another section of the twist was lightly sanded and repolished, as shown in the last picture.

Making a rotary burnisher from an Allen key

2009-12-02T17:12:00.000Z

After a tip published in Orchid by J Morley in 2004, I used an alumina separating wheel to shorten the shorter end of a 7/64" Allen key to about 1cm, and used the same wheel to roughly grind the end to a dome. Later I discovered that this latter operation was probably a waste of time, a better way was to fit the Allen key into the pendent drill and rotate the cut end against progressively finer grades of wet abrasive paper. This had the great advantage of producing a profile (providing the drill was slowly lifted and lowered to additionally shape it in another plane) which is maximal size for burnishing. The result was a very attractive looking tool, requiring no heat treatment (the same tool can be made using a bur, but this requires heating, bending, shaping, re-hardening then tempering - a lot more work).
Unfortunately, actually using the tool is a different matter. I tried it on various old pieces of cast silver with porosity, and although it bashed the surface very satisfactorily, not all porosity was closed up, and I was uncertain how to finish the resultant surface. I tried the abrasive radial wheels which did indeed get a wonderful polish, but did not remove undulations in the surface caused by the rotary hammering effect. It is faintly possible that my method of getting a maximal size burnishing surface is at fault, perhaps a much smaller burnishing surface would get better results. Of course, I realise that if nothing else, it may be useful as a power texturing tool!

Making & using plaster gems with PMC

2009-11-23T18:21:00.002Z

Although CZ and many other gemstones can be successfully fired into PMC, I often find that the brilliance (at least of CZ) is slightly diminished by this process. So I made a flexible rubber mould of some 5.5x5.5mm CZ hearts, then cast the pavilions using a fairly hard casting plaster. Each tended to have a small missing piece at the point of the pavilion due to an air bubble, but this proved not to be a problem. When well dry, they were embedded at girdle height in plastic PMC shapes (themselves embedded in flexible rubber moulds), the whole de-moulded, dried and fired at 800C. This higher temperature possibly helped to denature the plaster sufficiently that it was easy to clean out from the cured (i.e. sintered) PMC. It would only remain then to set the coloured CZ hearts using a spot of glue. However that is not what I actually did - on a whim, I melted dichroic glass fragments into the heart-shaped cavities in some samples of the uncured PMC, whilst also firing some 15mm PMC heart shapes with 5.5mm heart-shaped coloured CZ embedded in the uncured (unsintered) silver. In the side-bar to the right, you will see examples of the fired-in-place CZ (right-most two hearts, amethyst and orange respectively) along with the left-most three specimens which had variously coloured dichroic glass pressed in them while red-hot and fluid.

Enamels on copper plate on silver

2009-10-27T18:14:00.002Z

Various pieces of PMC had areas that were electrolytically copper plated, then covered with areas of reptile green and ruby red transparent enamels. On firing the results were mediocre, however with hindsight I realise that I chose two unpromising colours - in particular reptile green goes brown on copper, rather than the beautiful green it goes on silver flux on copper. I then went on to embedding small copper shapes in PMC and applying enamel, though in most cases coping with the oxide was the biggest problem.

Detection of mercury vapour

2009-10-05T17:48:00.004+01:00

After some research in my chemistry books, I settled on cuprous iodide / silver iodide paste mixed with precipitated sulphur as a possible reagent. The reagent was made by double decomposition of silver nitrate and copper sulphate solutions added to a solution of potassium iodide. The resulting yellow paste was painted onto filter paper and allowed to dry. On exposing to mercury vapour in a glass vial, the exposed area turned a satisfying but not very visible light amber colour. I doubt that it would detect the vapour from the mercury spill which occurred some years ago in the kiln room...

Over-cooking enamels on fine silver...

2009-09-13T23:07:00.003+01:00

The first picture below is of a matrix of 6 rows (5 different transparent enamels from the top down, none on the bottom row) and 7 columns (6 different fluxes from the left, none on the rightmost) fired to completion at around 820C. The second picture is of the same specimen subsequently accidentally fired for another 10 minutes at around 850C. The five enamels were probably ruby, aqua, tangerine, reptile green and amethyst, all from the "professional jewellery enamel" range from Vitrum Signum.

Thermochromic enamels

2009-09-10T21:34:00.009+01:00

Anyone using enamels would soon find that some are thermochromic, displaying different colours at different temperatures. The pictures below show the transitions of two different enamel colours on fine silver; the outer corner squares and the central square were enamelled with transparent reptile green, the remaining areas in transparent ruby.

From this one can see that when red hot, not surprisingly the whole mass glows; then, on cooling, the reptile green areas turn from red to black (perhaps about 400C?), next turning to amber (around 250C?), then yellow/grey/green (not illustrated, around 150C) before becoming a rich green when cold. The ruby however, although reasonably pink after a single firing, when fired several times becomes progressively more and more grey, finishing (as here) in strange fibrous opaque clay-like swirls.

Detection of lead in dust samples

2009-08-24T17:56:00.002+01:00

I relied on literature in school chemistry books which proposed acetic acid. Once dissolved, the presence of lead is easily detected by adding a solution of a dilute soluble sulphide or polysulphide, giving a dark-brown / black precipitate of lead sulphide. However in my experiments with small fragments of cleaned lead strip, I found it did not dissolve in acetic acid even in high concentrations over a period of 8 hours. Heavily corroded lead also did not dissolve. Further reading suggested that dissolved atmospheric oxygen is required. Adding a small amount of hydrogen peroxide rendered all lead and at least some corrosion compounds readily and rapidly soluble in acetic acid solution. The problem now is that any precipitate of lead sulphide tended to get oxidised to white lead sulphate by surplus peroxide, compromising and complicating the original test scheme. However I did manage to show the presence of lead in 0.1% lead acetate solution used as a control , although it was more problematic in 0.01% solution.

Dichroic glass on 'liquid enamels'

2009-05-29T17:59:00.003+01:00

A rolled-out copper coin (i.e. rolled with a jewellery mill to remove the pattern and give more real estate to work on) was dipped in 'liquid flux', a powder which I mixed with distilled water to a suitable consistency. It was then fired, giving an unusually smooth and glossy clear coat. I then gave it a layer of 'liquid white', mixed from powder in the same way. Both powders had been bought from Vitrum Signum a year or so ago, awaiting a suitable time for experiment.

On firing, there was a pleasant smooth slightly matte white coating. To liven things up, I painted some little dashes of cobalt oxide in water into the surface, staining it with some dark blue patches. These remained matte through one or two more firings before starting to become glossy, presumably through vitreous material making its way through the surface oxide. Finally I laid a piece of dichroic glass on the enamel and fired that; on cooling, I found that I could 'pop' the top layer of glass from the dichroic, leaving an iridescent coating on the coin. Also, a significant amount of the white had been gradually dissolving into the clear flux below, leaving a bright image of the coin beneath.
The second piece, a small rectangle of copper with unwanted enamel experiments, was also treated to a small rectangle of dichroic glass fused to the surface. Or rather, two pieces, but the right-hand one slid off in the furnace.

The eyes have it...

2009-05-04T21:28:00.006+01:00

The piece on the left is plain fine silver (from a rolled-out fine silver casting grain) with a faint leaf-vein pattern hammered in, and some enamel on to test colours. It was very boring, so I fused a pair of fine-silver eyes with purple enamel to the surface.
The right-hand piece is again fine silver, PMC this time, moulded from a real leaf (starberry). This gave the veins in reverse which was more attractive than the original. After enamelling, I thought it also benefitted from a pair of eyes, perhaps I've just seen too many cast leaves...

Glass enamels

2009-05-01T22:42:00.006+01:00

I found a few pots of "glass enamels" which I had bought some two or three years earlier from a company called Potterycrafts, when I was thinking of doing some more glass fusing. Checking in the catalogue, I found that the firing temperature was just under 600C. Five samples were made, and two illustrated below;

I added a semi-abstract semi-pastoral image in primary red, blue and yellow to a discarded piece of copper which had a grey enamel surface, and fired it at 800C, out of curiosity. To my surprise, the colours didn't burn out, but gave the image shown. A second enamel piece, this time with a rather nice abstract leopard-skin pattern, had some spots added in the same primary colours, and fired at 600C. The result is the piece in orange / brown with darker spots.

The glass enamels were extremely easy to paint after adding enough distilled water to make a thin cream; so I am considering getting some "painting enamels" if possible, which are presumably equally painterly in effect and intended to be compatible with metal rather than glass. There have been no signs of distress on the enamels above.

Burn-out time

2009-03-08T22:42:00.001Z

The final part of the Winter courses casting component meant that I carefully packed 20 ceramic shells in expanded polystyrene chips inside a couple of large square plastic boxes (both originally held Turkish dondorma!), and carted them off in the train to the workshop near Wimbledon.The weather was very cold, somewhat breezy but clear when I got the furnace dome set up and the task of burning out the waxes underway. To my dismay, of the 60 or so items on top of the shells, around 9 came to some kind of grief, although later about half of these were to be repaired at least to some extent. Unfortunately one of the casualties was the wax of a 12cm pig, intended to be cast in silicon bronze. This gave an audible loud ‘pop’ inside the furnace dome, breaking into four or so large pieces.My feeling is that the increased failure rate (about double the usual) is probably related in some way to the temperature at which the waxes had been stored, and that at which the burn-out took place. However in at least one case, the failure was due to the fact that a collection of items on a shell had insulated the outlet wax stalk from the heat; the expanding wax had nowhere to go but out through the top, bursting it off. This particular item was later given a repair.I wondered, as on several occasions in the past, if the number of failures could be reduced with strategic additional 'sprues' intended to allow leakage of wax during burn-out.

Carving hard plaster

2009-02-14T22:40:00.000Z

I have a series of small plaster figures, each more than 5 years old, which I would like to modify and hopefully improve before recasting in bronze or other metal. The plaster was an alpha-hemihydrate type, hence very hard. I found it carves rather nicely, but slowly, with an HSS burr in a pendent drill. This leaves chatter and other tool marks on the surface of the plaster, but frequently I found these marks rather appealing. It also ‘carves’ well with a small coarse alumina-composition grinding tool in a pendent drill. Various shapes are available, unfortunately I find that the smaller and more precise shapes are a less coarse compound and take longer to cut.
Having some of the old rubber moulds available, which I made around the same time, I tried pouring copies in a much softer (’potters’) plaster, but the incidence of air bubbles was so high as to make the casts nearly useless. I expect that if the unset mix, and subsequently the moulds containing the freshly-poured mix, were subject to reduced pressure with a vacuum pump, they may become just what I need. Unfortunately I mislaid my aspirator some time ago, and this kind of cheap and effective pump now seems difficult to find.

Removing enamel with molten alkali

2008-12-11T11:22:00.006Z

The details for removing enamel with molten lye are frequently kept hidden on the grounds that the technique is dangerous. My own assessment is that it is comparably dangerous to leaving work on Oxford Street in London on winter evenings, given suitable safety training for both activities. Other people's assessment may differ.
I cooked the object with the enamelled areas covered with about an equal volume of anhydrous sodium hydroxide ('caustic soda' or 'lye'), at about 400ºC (which is above the melting point of about 360ºC), in a tiny iron container (an old pot lid) in a small enamel kiln. I imagine a tiny copper pot would work perfectly well. The molten lye dissolved the enamel within minutes, and was then allowed to cool when it set rather rapidly into a grey-green mass. When sufficiently cold I irrigated it with a large amount (a bucketful) of cold then boiling water to dissolve the caustic soda together with reaction products. Usually I found that the enamelled object would be stuck to the pot with solid lye underneath, hence the boiling water to help dissolve it quickly.
See the footnote to this website for the disclaimer concerning safety! Lye is very caustic to skin (and in fact all human tissue) even at low concentrations and temperatures, so I wore goggles and rubber gloves. Solid cold lye can misbehave with water since it is an exothermic reaction, and I found that molten lye misbehaves even worse (explosively possibly) with even very small quantities of lye - hence the reason for waiting until all reaction products are cold, to avoid the risk of splattering hot caustic alkali around. Good ventilation is required - a small amount of injurious alkaline spray is produced which one wouldn't want to breathe in, and more if the alkali is not cold when added to water.
But, the pay off - the vast majority or all of the enamel simply dissolved away, and in those cases where some remained, it was removed by drying carefully then repeating the operation.
An alternative technique uses an aqueous paste of sodium chloride (common table salt) and potassium sodium tartrate (Rochelle Salt), applied to the enamel areas, then the whole heated to 750ºC. It is then plunged into cold water ('ice cold' is recommended on various sites). I found this was occasionally very successful, but sometimes only as good as plunging red hot enamel into cold water, and that it often never removed all the enamel even after repeated application. The use of such high temperatures and high temperature gradients on quenching is also likely to be problematic in some cases, causing warping for example. The chemistry involved seems to be unknown - the enamel is not dissolved, but seems to break away from the substrate more easily.
I also briefly experimented with molten potassium hydroxide for removing enamel with satisfactory results. The melting point is similar to that for the sodium salt; and the boiling points, at above 1300ºC for both, are sufficiently high to guarantee a stable temperature region of molten alkali. The potassium salt is of course potentially more reactive, and poses greater safety risks. It didn't seem to improve the removal of enamel, but was more effective than the sodium salt at removing ceramic shell investment from an old bronze specimen I had had lying around for a few years. As expected, it also severely degrades glass.

Meccano meets Anglepoise

2008-10-18T22:31:00.006+01:00

I have only had time for a few small tinkerings over the past couple of weeks; these included trying to cast pewter in a way that embeds copper alloys for contrast (the idea came from Oppi Untracht's book and mostly failed, I need a means to secure the copper to the walls of the mold first); carving a design into a gesso panel using standard gravers (went very easily when the gesso was dampened); carving a discarded slab of leather-hard clay into a primitive Gothic arch; and making a very "Heath Robinson"-contraption to help when hand or machine grinding of cabs and other stones requiring a precision flat face. Well, if not precision, then at least not rounded too much. In use, the stone is attached to the base of the left-hand vertical of the jig with setter's wax or similar, the right-hand vertical is ideally screwed to a work bench or immobilised with a weight on top, and the parallelogram arrangement ensures that the lateral grinding action of one's hand is regularised to prevent rounding of the bottom face of the stone. And it works, and even better when the stone is actually on a lapidary wheel. I imagine professional lapidary wheels have a rather better jig built-in. The white blob riding on the sandpaper is actually a thermoplastic, which is a very bad idea since it is as tough as nylon and greatly impedes sanding / grinding; setter's wax worked much better, both by hand and on a flat lap. I have actually thought of what might well be a better system for hand grinding on wet-and-dry, but not got around to making it yet.

A brief holiday

2008-09-26T22:28:00.003+01:00

From 4th to 16th September I had a holiday in southern Turkey; mostly staying in Antalya, with a day at Phaselis, and 4 days at Kaş, all three on the coast. Very enjoyable, it's been a long time since I had more than a long weekend anywhere, although I never acclimatized very well to the daytime temperatures of 39C (or the night-time ones of about 28C). My thanks go to Kemal Özkurt of The Owl Bookshop, and to Harun Enez and Hussein Enez of Boncuk Bazaar (both in the Kaleiçi in Antalya) for looking after us so well.
Anyway, I found to my surprise that my brain performed noticeably better than it usually does (as measured by scores on Sudoku and Bobby Carrot [a Java game on my mobile], and remembering events for my diary!) which highlit the extent to which I have been flogging the poor thing.
Perhaps now I'll have the energy to actually make something, instead of watching others make things.

Silicon bronze strip

2008-08-18T16:11:00.005+01:00

By way of entertainment I soldered some scrap pieces of silicon bronze strip to some equally scrappy pieces of sterling silver.The result was then pushed through the rolling mill with some copper mesh to texture, and the surface subsequently polished a little. It looks as though it will be very suitable for suggesting to students for two-coloured rings. One caveat is that silicon bronze tarnishes rather rapidly when worn by some people, including myself. I subsequently found that some craft plastic mesh, so fine as to be almost transparent, was as good at putting an impression on the metal when rolled through the mill. My reading of Oppi Untracht's texts suggests this is perhaps a simple version of 'married metals'.

From chisels to gravers

2008-07-14T23:51:00.001+01:00

Another staff development course financed by Central YMCA, I attended the first day of Working with Stone with Charlotte de Syllas as tutor, and the four days of Engraving with Wayne Parrot and Alan Craxford, both courses being held at the Sir John Cass Department of Art, Media & Design within London Metropolitan University. If time, timetable and cash had been on my side, I would ideally have also liked to do the remaining four days with Charlotte. Perhaps next time. I have already done quite a bit of lapidary work, and made a good start on fashioning a lacy agate cover for a cast silicon bronze seashell (pictures soon).
Engraving however is something I have not tried before, although I have used gravers for raising beads in pave work, and the main impetus for attending this course was to get to grips with gravers, as it were. I still regard them as one of the most difficult metal-working tools to do useful things with, and fortunately this course gave a good grounding for a beginner like myself, although it was really aimed at those who had already done a three day intro or had had some experience. But I started the course after talking to the Director, Alan Craxford, and things seemed to work out quite well. Wayne Parrot seems to be one of the few traditional fully-trained and experienced engravers around, and made an excellent tutor. Pictured below is my first crude attempt...

More work with enamels

2008-06-23T23:12:00.007+01:00

After the end of term (apart from a Friday sculpture class) I had enough spare time to tinker with some enamels. Some 'bronze' 2p pieces were rolled a little to reduce the surface detail, with annealing as required. These particular 2p pieces are now becoming uncommon; more modern ones are actually made of steel with an outermost thin layer of copper alloy. I use a magnet to separate them out. A 1.5mm steel wire was polished with sand paper then coiled into a shephard's crook sort of shape, and used between two of these rolled bronze coins to impress the design when the sandwich was again rolled through the mill. For good measure, I repeated the trick with two squares of 1.5mm annealed copper. I had intended to use these for enamel tests - see the picture in the right-hand bar.Another two bronze coins, again rolled to reduce the amount of relief design on the surface, were drifted with diamond flux before firing. Then a piece of coarse metal mesh was laid on top and opaque white enamel powder drifted on top. The mesh was carefully removed and the result fired, to give a nice regular array of bumps in white. It was then re-fired sufficiently hot to cause the diamond flux to bubble up under the white and give a beautiful sparkling gold appearance. Other areas went green / black, probably some interaction between the flux and copper oxide (i.e. scale from the first firings). See picture in the right-hand bar.

Making a silicon-bronze ring III

2008-05-05T20:22:00.005+01:00

Although the rolled-out 0.5mm silicon bronze in part II below seemed perfectly acceptable for a ring liner, I thought I would substitute some of the fine silver I had recovered from sterling scrap. The thinking was that it was softer and would be easier to tinker with by hammering; also there would be a colour contrast, and less chance of copper staining for the wearer!
The picture on blue felt shows the colours better, but also shows that I hammered the side face of the silver liner with a '0' numeral punch (the only type of small punch I possess). If nothing else, it shows that it is high time I bought or made some suitable small punches. The second picture shows the reverse, where the rivetting of the inner fine silver liner was done by hammering a conical mandrel into the ring, then burnishing the lip over for the last fraction of a millimetre. Fun, but I need to try a few more to refine my technique.

Making a silicon-bronze ring II

2008-04-20T21:14:00.000+01:00

The insert for the ring was originally made of silicon bronze strip 13 x 0.5mm after rolling. This was cut nearly to size and rolled round in a ring former. It was then slipped inside the domed ring and the butt edge scratched with a scriber to give some idea of where to cut. In fact, I found one needed to allow about 0.8mm to get a perfect fit. It was soldered with hard solder in a similar iron wire ring to that for the dome, but smaller in diameter. An even larger gauge iron wire, springy and very tough, was used to pull this ring apart during heating to re-adjust the solder seam – very inventive, but not quite inventive enough since the ring went shooting off into the room. After re-soldering, pickling and cleaning, it was a nice fit in the domed ring.
However I felt it was unnecessarily heavy, so repeated the process of making a plain band with 13 x 0.25mm silicon bronze strip. In all cases for this project, repeated use was made of the enamel kiln set to about 800ºC for annealing. This satisfactorily softened the metal, but the darkened surface was quite resistant to removal even with hot acid, taking additional scrubbing with wire wool. Subsequently, I felt that I should remake the inner band a third time, this time wider, so that it could be riveted up the sides – the extended rim looked nice.

Making a silicon-bronze ring I

2008-04-16T19:15:00.000+01:00

I cut two rectangular strips of silicon bronze, 37 x 1 x 12mm, then wished I had super-glued them together for the subsequent filing square of the ends and the long ends. The original stock strip was 1.5mm, annealed and pickled, rinsed and washed, then rolled to 1mm. It was a great help to hold the emerging end of the strip with parallel pliers as it came from the rollers, my hand holding the pliers elevated with a suitable board and movement facilitated with a sheet of plastic underneath. Even better probably would be a suitable emergence table at the exact right height. I used dividers to mark the strip, at 37mm and 38mm for sawing in between; and placed a strip of balsa wood on the bench peg to help steady the strip for sawing. This was done twice to give two rectangular pieces 37 x 12 x 1mm, they were superglued together and left until dry in the vice. Then they were filed as necessary for squareness, before placing in the enamel kiln at dull red heat to break the bond and anneal.
For doming, I bent a piece with pliers until it fitted into the largest dome, domed it, and repeated until I had reached the 26mm dome, the smallest hollow that this size strip would still fit inside. The strip, on bending slightly, now sat in the 25mm dome with 2mm protruding, therefore there was a line inset 2mm from the edge caused by the last doming operation. The resultant ring was oval at 25 x 25.5mm. Sanding the short edges by holding them flat on sandpaper (painful on the fingers, especially if using a steel block to try and ensure registration with the other dimension) got it to a nice circle at 25mm diameter. My feeling is that using the steel block is a waste of time, and doesn’t help any kind of squaring operation. However it is possible that the rounding of the corners of the short edges using the block was entirely due to swapping faces pressed against the block, without having taken steps to absolutely guarantee that the two faces are exactly parallel. So I suggest use face A on block, edge on sandpaper; then edge on block, face A on sandpaper; then edge on block, face B on sandpaper; but never face B on block and edge on sandpaper – this would accumulate an error! Mark near face B with ink to reduce the chance of a mistake.
For soldering, I hit on a happy idea – a circle of strong steel wire stuck out in space, the two halves of the ring aligned and dropped into this slightly smaller circle to merely sit there. Then solder from the base – this worked perfectly.

Cleaning sterling grains

2008-04-12T21:02:00.000+01:00

The sterling grains I had made (by re-melting and pouring into water about 500g of silver from a previous failed casting venture), gradually looked very dirty on the surface. They were steeped in sodium carbonate solution sat on aluminium foil for some days, which made them noticeably worse. Subsequent steeping in sulphuric acid made no change; nor permanganate, peroxide or bisulphite! I melted one of the larger lumps with some borax to get an interesting set of colours; white as in clean sterling on the part in contact with the crucible bottom, black on most of the top as in oxidised sterling, and a fluorescent yellow / green (which had been very golden in colour when red hot) on part of the top, possibly caused by the borax flux. The lump of silver was dumped in sulphuric acid for a couple of hours. Incidentally, these grains had been satisfactorily used to cast student work in early spring.
Subsequently I placed all the remaining tarnished grains in a ceramic shell open mould and set it in the enamel kiln at around 800°C and left it to reach dull red heat. On removal, as hoped, the surface of all the grains had changed from a kind of creamy mushroom grey to dark grey. They were cooled and dumped into dilute sulphuric acid, which satisfactorily converted the surface into the kind of clean white I associate with sterling silver.

Etching glass III

2008-03-10T09:18:00.004Z

A surprise shipment of ammonium bifluoride meant that I spent another hour re-masking some frosted glass with Sellotape, adding a design in nail varnish, then sealing it into a plastic tub containing 10% sulphuric acid with 20% of the new bifluoride.
The equation for solution of silica in hydrofluoric acid is generally given as
SiO₂(s) +6HF(aq) → H₂SiF₆(aq)+2H₂O(l)
The result is fluorosilicic acid. After an hour it was obvious that ammonium bifluoride was, as expected, a much stronger etching agent than the sodium salt. However the demands of administration of courses for next term (starting 14th April) mean that I will have to shelve the project for a few days at least.

Etching glass II

2008-02-24T22:09:00.005Z

A small piece of window glass was uniformly frosted with 45 micron diamond powder made into a paste with glycerine (using a flat glass muller) then washed and dried. The reverse was masked with Sellotape, and a design painted on the front with nail varnish. After thorough drying, it was re-etched by immersion in 15% sulphuric acid with about 10% sodium bifluoride added, in a sealed plastic container for about 24 hours.
The results after this time were disappointing, with no apparent change in the frosting when wet. After washing and drying, again there seemed little change in the frosting - at least for the first few minutes! After that, to my astonishment, a dendritic growth of what seemed to be white crystalline material appeared over the whole of the exposed glass surface, taking about 5 minutes to cover it entirely. On scraping with a blunt plastic tool, it was found to be some kind of loose surface material, presumably silica-based. It was again washed, and the masking agents removed. This plainly showed a difference in the etching texture given by diamond paste compared with the chemical etch. I need to research the nature of silica degradation by bifluoride!

Etching glass I

2008-02-21T09:46:00.005Z

I like equally the effect of both etched metal and etched glass. But the latter requires use of hydrofluoric acid or equivalents, which is not fun to use at all. It demands a fume cupboard and a professional approach to personal protection equipment.
So I have been experimenting with a potentially safer alternative, namely bifluoride salts. Unfortunately I have not been able to find a supplier of ammonium bifluoride, the salt of choice because of its high solubility in water. Instead I have to make do with sodium bifluoride, which has very limited solubility.
My present interest is in 'bite & grind' which refers to etching a design onto sheet glass, and grinding the design in selected areas with a flat glass pad loaded with diamond abrasive and glycerine as a lubricant. Sometimes one might use 'grind & bite' instead.
Work is going slowly at the moment since this is the middle of the spring term and most of my time is taken up with teaching and administration; and early next week is scheduled as the 'casting days' for two different classes, using silicon bronze, silver and pewter depending on the students' interest.

Tree of life

2008-01-06T22:40:00.000Z

My favourite organisational concept (a tree, that is). After a sleepless night (the result of too much Xmas cake probably), I woke up with a desire to fire up the old Bloodshed Dev-C compiler on the laptop. One of my university lecturing specialities before I retired, was teaching algorithms & programming techniques. So, designed a nice recursive Win32 tree program (more entertaining than Sudoku), and spent some hours tinkering with it until I liked the details. Squished it with Gimp (open-source graphics software), annotated it with my original blog title and sub-title, and replaced the old blog pic with this new & perhaps rather apocalyptic version.

For those readers not familiar with recursion, it is a method of specifying an algorithm or procedure that invokes the algorithm itself within the body of the specification. An oft-quoted example is "...and God created man in his own image..." which could be criticised (somewhat tongue-in-cheek) as having various defects when matched against the humdrum requirements of computers; it has no stop condition, does not anywhere reduce to an element which can actually be created (or indeed change in any way at all), has no clearly specified engine to run the algorithm on...

November blues

2007-12-14T17:43:00.000Z

Our previous term of 8-week courses came to an end four weeks ago, and I have found myself tied to the desk planning the next session which starts week beginning January 14th. As a result, I have had no time for my usual workshop activities. In addition, we have been moving our Wandsworth production workshop (which was in an old factory, now scheduled for demolition) to a smaller unit nearer Wimbledon, and that has sucked up all the remaining time. And I still have to get myself organised to buy student stuff for next term's courses, and update my student's work blog site.

Classical head

2007-12-02T21:47:00.003Z

I decided it was time to do a little rescue work on a large clay head I had made (8 times life size) in the general style of a classical male. It was originally designed lying nearly prone, in a kind of sleeping pose, but was never cast in that pose.
I moved it back to the upright to try and remove some of the staining from slip (quite a bit of ceramic work goes on nearby!) before casting. The background on the final picture was processed in Gimp, and I seem to have accidentally bent the aspect ratio a little.

If at first you don't succeed...

2007-11-17T18:00:00.000Z

Since by now I was in love with the aqua blue transparent enamel on fine silver, I prepared another rectangle of the silver but only 0.5mm thick, and textured it as before with an automatic centre punch, producing a crude heart design. Then I bent some filigree wire into the same heart-shaped design and applied it to the sheet to lie flat. This time also, I bent the wire so that the larger dimension of the cross section was made to lie parallel to the sheet, so that on sanding, the filigree wouldn't tend to fall apart. In the previous effort, it had stood up the other way on the backing sheet, making it too tall, and also prone to falling apart at the links if sanded thinner.

Some washed aqua blue enamel powder was drifted into the design and fired until it melted; but alas, by now the fine silver was too fine to allow rough handling (e.g. during sanding or stoning of the surface) so that bits of the enamel were prone to crack off. I solved this by cracking the majority of it off by a mixture of flexing and quenching from dull red heat, then domed the ensemble of heart and backing sheet, using an ordinary doming punch and doming block. This had the wonderful side effect of 'pin cushioning' the heart design into the filigree.

The domed design was then re-filled with enamel and fired, with very pleasing results. Not perfect, but interesting. For the sake of some colour contrast, I drifted 'nectarine' enamel round the outside, removing surplus from the blue or raised silver areas with a fine brush, and re-fired.

Final step - removing the sharp corners of the domed rectangular sheet, since the doming process had turned the corners into sharp spikes.

Overall opinion - a bit amateurish, but there are many possibilities for improvement:
- use a border of silver wire to contain the nectarine colour
- form a small heart in brass, roll this together with fine silver sheet in a sandwich to emboss the design into the sheet instead of the doming block method
- mitre the ends of the fine silver filigree wire so they don't form such an ugly angle

P.S. The picture above is larger than life size - the actual size is about that of a UK 5p piece.

Enamel on fine silver

2007-11-14T12:26:00.000Z

Since it was some time since I have messed around with enamel, I thought I would give it a try using the fine silver I prepared earlier, as it were.

A small piece about 10 x 10 x 1mm was given a surface texture of dimples using an automatic centre punch, and given a walled enclosure with some fine silver filigree wire. This wire was made according to the instructions in the book by Jeanne Rhodes-Moen. The enclosure was in the shape of a heart. I then packed the enclosure with 'aqua blue' transparent enamel made by Milton Enamels in the UK.

Since our enamel kiln finally expired a couple of years ago after years of use and abuse, I fired the prepared piece of silver on top of some iron mesh with a small blow-torch underneath. This particular enamel turns first green then finally black as it melts; when it cools, the colours neatly reverse through green back to a very nice blue, effectively gluing the silver filigree design to the backing sheet. In passing it occurred to me that using a copper backing sheet would have allowed me to remove it by dissolving in acid, ending up with plique a jour.

Then I ground the surface down using wet silicon carbide paper, cleaned it off with a glass fibre brush under running water, and re-fired after packing one or two areas that were a little short of enamel. The grinding and cleaning was repeated, and the piece inspected.

Here was where things started to go wrong! Since I felt the enamel needed more building up in one or two areas, and since the colour was on the dark side and hence obscured the dimple texture underneath, I thought that some clear enamel on the top would be a good idea. Unfortunately I probably chose exactly the wrong clear enamel, in the form of 'super soft'. This in fact not only melted quickly into the missing areas, but fluxed the aqua enamel so much that both 'super soft' (in the form of a yellowish glaze) and aqua started to leak from the bottom of the filigree enclosure.

So, back to the drawing board. Pictures later!

Etching with peroxide

2007-10-27T21:42:00.001+01:00

I have done quite a bit of plain chemical etching of copper alloys and sterling silver, using ferric chloride/citric acid as the etching agent for the copper, and ferric nitrate as etching agent for the silver.

My preferred method however is to use electro-etching, with the object to be etched connected to the positive terminal of a 12v dc supply, and a stainless steel, silver or graphite cathode. In these cases, I use a series of 12v bulbs in parallel with each other as a controllable load.

In the case of electro-etching, the etching agency is a combination of the electric current and the liquid it is immersed in, the electrolyte. As a result, there are more options for the liquid than in the case of chemical etching.

At its simplest, the electrolyte could be distilled water - this conducts electricity to a negligible degree and hence the etch rate is negligibly small. But not zero - see my notes about colloidal silver. The next available option is to use a salt of the metal to be etched - copper sulphate in the case of copper alloys, and silver nitrate in the case of sterling silver. Not only do these work well, they have the terrific advantage of not being sufficiently corrosive to damage the usual resists used in etching. Unfortunately, silver nitrate is hugely staining of skin and just about everything else, especially after exposure to sunlight!

However, being the impatient type, I am usually interested in getting the fastest and most accurate etch, so I experiment now and again with different electrolytes. This has included using the aggressive chemical etch solutions mentioned above, augmented with the electric current.

The most recent experiment was etching copper using copper chloride solution, augmented with hydrochloric acid and hydrogen peroxide. Copper doesn't normally dissolve in hydrochloric acid unless there is dissolved oxygen present; this requirement is met very well by adding the peroxide, which enables rapid dissolution of the copper. It has the advantage of being a clear liquid (apple green in colour) unlike the ferric chloride-based solutions which are murky and completely opaque. The disadvantage is that the liquid would be expected to be somewhat more corrosive to the resist.

At any rate, I let a piece of copper, about 20 x 80mm, protected on the rear and sides with nail varnish as a resist, and the same for a design on the front, etch for around an hour. The results were very satisfying with an etch of around 0.5mm, though with quite a bit of break-through of the resist. Also, since I had no means at the time to provide agitation, there was a ripple pattern in the etched metal, somewhat reminiscent of (and perhaps related to) the ripples left on a beach by the receding tide.

My first attempt at making colloidal silver

2007-10-16T23:37:00.000+01:00

After rolling out some of the presumed fine silver made earlier, I saved some for making bands etc and still had two large strips which I thought I would try and use for making colloidal silver. I immersed two such strips in distilled water in a clean plastic container, and connected them to a 12v dc supply via a system of 6 12v bulbs, all in parallel. This is the system I use for etching and other related operations.

I left it running for several hours, with no visible light from the filament of the single bulb I had in the circuit (by unscrewing bulbs I can reduce the maximum current that can flow). But both slabs of silver darkened, rather considerably, and additionally I think there was a fine, faint fog of black silver particles in the water.

I tried a trick I found on the Internet, namely shining a simple laser pointer through the water; this plainly showed the path of the laser, giving some confidence that some at least of the silver was converting to colloidal form! I checked that the laser also showed such a beam when passed through colloidal silica solution, and no beam when passed through plain water.

Refining scrap silver

2007-10-10T16:04:00.002+01:00

I had 300g of impure sterling silver. This resulted from a mould leak in the bottom of my furnace, so I re-melted the salvaged metal and poured it as grain into water. Subsequent testing indicated that it was probably too impure to use - not surprising considering that the same furnace is used for casting leaded bronze, and that has also leaked on occasion!

300g of this impure silver was added to 150ml distilled water and 300ml commercial nitric acid in a flask with reflux tube; the bottom of this went below some sodium bicarbonate and diluted ammonia solution. It was initially cooled with a water bath to reduce the output of fumes, and then later heated in the same way (to speed up the reaction). The sodium bicarbonate seems to be irrelevant – and the container of dilute ammonia solution should be placed in a larger container holding more ammonia since the white bursting bubbles actually contain some orange gas.

Subsequently I found that one can better scrub NOx gasses in either 10% sodium hydroxide + 3.5% hydrogen peroxide (Nikon process) or 0.2% hydrogen peroxide and 10% nitric acid (Kanto Denka process). An intriguing remark from www.h2o2.com suggested that peroxide could be added to nitric acid in many metal pickling applications, thereby removing NOx at source and regenerating the acid.

After about 40 minutes when bubbling was very slow, the nitric acid / silver nitrate solution was filtered, the excess silver washed and retained, and the silver then precipitated from the liquid with salt (sodium chloride) solution. After a false start doing filtration, I then continued by decanting the liquid and rinsing the white precipitate with boiling water several times, until there was no blue colouration with ammonia (which would be caused by any copper contamination).

On standing, this white sludge would slowly develop a violet-grey surface due to the action of light. I initially tried reducing the silver chloride to silver with aluminium wire and hydrochloric acid; this caused some continuous darkening as silver was precipitated, but seemed very slow and to require much more wire and time. So the wire was removed, the sludge well washed, then finally had 60g dry sodium hydroxide and 30g dry glucose powder added. The glucose was caramelised (judging by the smell) and the sludge turned more or less unevenly grey with pink-grey parts as the chloride was reduced to silver (and regenerating salt solution I imagine). After well washing, I decided to repeat the process, which got rid of the pink grey parts.
After drying, the final result of my labours was a large number of silver stains on workroom surfaces (and fingers), and about 280g of fine light-grey granules, looking very like cement powder. It took a lot of Internet research to find a suitable way of removing the afore-mentioned stains - in the end I used acidified potassium permanganate followed by acidified sodium bisulphite solutions.

280g of this powder after drying was packed into a ceramic shell crucible with a large lump of coke, and heated in a propane-fuelled furnace for 15 minutes to around 1000C. This resulted in the evolution of large amounts of what was almost certainly chlorine and / or hydrogen chloride, which required ammonia solution in the workroom to help neutralize it. Fortunately I was wearing an adequate mask. Additionally, there was a constant rather large blue and green-blue flame coming from the top of the furnace, something that doesn't normally happen.

The crucible was removed, quenched and broken apart to reveal my two slab castings each about 5mm thick, totalling only 260g – so potentially there may have been up to 20g of chlorine present as chloride or otherwise! A strip of one slab, about 10mm wide, was rolled down to 1.5mm, showing that work hardening was very minimal – even rolling a slab 50mm wide was quite easy in a rolling mill without gears. Two large cavities at the upper ends of the slabs had very intriguing triangular ‘bird foot’ shapes made of minute granules – presumably some kind of crystallization phenomenon. They were so intriguing that I decided to keep them, and added the attached pictures. The one above on the left is a plan view, and the one below on the right is a near-elevation, showing 5 stubs radiating from the centre of a 3-axis structure. The sixth runs into the body of the silver. I guess these would make sense for something belonging to the face-centred cubic system, crystallising from the centre along perpendiculars to each of the six faces of a cube.

One of my diversions...

2007-10-04T13:34:00.000+01:00

No, honestly, I've absolutely nothing against arms and legs...

I spent a few years designing, sculpting and manufacturing a range of small torsos (between about 9 and 22" high) for a London gallery and various art fairs and shows (e.g. Battersea Arts Fair, Affordable Art Show etc). These three were pictured in a gallery brochure.