There were three basic groups of synthetic pigment used in Ancient Egypt: powdered glass, corrosion products, or those altered through the application of heat.
Egyptian Blue, a Special Kind of Glass
Possibly the most famous of all synthetic pigments made in Ancient Egypt it is still known today as Egyptian Blue. The pigment, a likely result of Ancient Egyptian glass or pottery glaze technology, is created by heating quartz (desert sand), calcium (limestone), small amounts of alkali (plant ash, potash, or the desert salt 'natron') and copper carbonate (particularly malachite) to a temperature of around 900°C and then maintaining it at between 800 to 900°C for several hours. Various blue tones, from a rich dark blue which was used as an alternative for lapis lazuli, to a pale, almost turquoise blue, could be created by either varying the proportion of alkali to copper in the mix, or by varying the degree to which the pigment was crushed (coarse ground – dark blue; fine ground – pale blue). If you are wondering how the Ancient Egyptian technicians managed to get the temperature in the kiln correct, the key is that they were proficient at producing bronze (used for tools and weapons) which has a melting point of around 870°C.
Color Technology in Ancient Egypt Using Corrosion
Two synthetic pigments were created through corrosion: verdigris and lead white. When copper plates are subjected to acid fumes, a rust, or patina, is formed. This rust, verdigris, can be used for a blue-green pigment. The corrosion process was quite lengthy since the strongest acid available to the Ancient Egyptians was vinegar.
Similarly lead white was created by corroding lead plate. A fairly complicated arrangement of earthenware pots split into two chambers was used. The two chambers allowed for the lead plates and the vinegar to be held separately. Heat was applied by surrounding the pots, whose tops were covered with an open grill, with fermenting animal dung or rotting tree bark. Vinegar (acetic acid) fumes would react with the lead plate to produce lead acetate. A further reaction with carbonic acid, from the dung, would produce a crust of lead carbonate – lead white. As with the verdigris, the process was very slow, taking several months to produce a viable amount of pigment.
Color Technology in Ancient Egypt Using Heat
Lead white was further transformed by reaction with antimony oxide, under heat, to form lead antimonite, a pale yellow pigment known today as Naples yellow (for the hue rather than the chemical composition). Heating lead white on its own would produce another form of lead oxide – red lead (known in medieval times as minium).
An Egyptian Legacy
Lead white, minium, Egyptian Blue, and other Ancient Egyptian pigments continued to be used in quantity by artists during the medieval and renaissance eras. Minium was so expensive, that it gave rise to the term miniature – a small painting, made so small because of the cost of the red paint used in painting it. Even today, traditional oil painters that were available to Ancient Egyptian artists.
For more about what color meant to Ancient Egyptians see Color in Ancient Egypt.
Color Technology in Ancient Egypt Part 1: Animal, Vegetable, Mineral
