Over-cooking enamels on fine silver...

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

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.