Why Djoser’s blue Egyptian faience tiles are not blue?
Manufacturing Djoser’s faience tiles at temperatures as low as 250°C?
30,000 blue faience tiles were found in Djoser’s funerary complex at Saqqarah (3. dynasty). It is generally assumed that the tiles underwent a self-glazing process during firing in the range of 800-850°C or by dipping in a liquid glaze. It is striking to notice that in contrary to their labelling, numerous Djoser’s tiles are not blue but grey, black, blue-green and even brown as displayed in figure 1.
SEM microanalysis shows the presence of phosphorus in the glaze that suggests the use of the blue mineral turquoise (mafkat), an aluminium-copper phosphate, intensively extracted by pharaoh Djoser in the Sinai mines. Our aim was to replicate the self-glazing process with a soluble silicate binder (a geopolymer glaze) involving a synthetic turquoise (mafkat) mixture made of pure aluminium phosphate hydrate and copper phosphate hydrate. We were astonished to get a turquoise blue-self-glazed ceramic, stable and identical to Egyptian faience, at a temperature as low as 250°C. Post treatment at 350°C changes the blue colour into grey-black (chemical transformation of blue copper phosphate into black tenorite CuO) that remains stable up to 800°C, where it turns back to blue. Did Djoser’s ceramists use this low temperature process? Apparently yes, if we look at all the colours that we have replicated at self-glazing temperatures in the range of 250-350°C
Considering the low relief/etch depth...and the repeating pattern in the Coffers you
Have presented in visual.
This suggests to me....that some are Geopolymer cast Coffers.
Numerous posts this forum on Geopolymer evidence /scientific proof....that Dynastic Egyptians were doing Geopolymer creations.
It may be that such items as Coffers** were an Investment/Prestige item...of the Elite
Or Crown Authorized Gift to favored person's.
The Geopolymer fabrication being a specialized production.