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.