In: Chemistry
Egyptian paste is a self-glazing ceramic body. In other words, the glaze materials are included in the clay body.
Working of Egyptian paste:
Egyptian paste is a ceramic body that includes soluble sodium carbonate. As the paste dries, the sodium carbonate migrates through the body to the surface of the piece, pulled by the action of water moving out of the piece as it dries.
Egyptian Paste
An Ancient Form of Pottery
By Beth Peterson
Pottery Expert
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Egyptian paste (also known as Egyptian faience) is a self-glazing ceramic body. In other words, the glaze materials are included in the clay body. No further glaze will be needed for the Egyptian paste piece to fire with a glossy glaze surface.
Two ancient Egyptian pottery hippos, photographed by nikoretro in the British Museum in London. Image Courtesy of nikoretro / Flickr
History of Egyptian Paste
Egyptian paste was first developed in the area surrounding the Nile River in northern Africa. Although unglazed pottery had been made here and in many other places in the world, Egyptian paste was the first pottery to have a glaze, rather than being left plain or painted with non-glaze pigments.
The discovery may have occurred when potters observed high sodium-bearing rocks fusing in their firing pits. Another possibility is that soda ash from the desert had gotten mixed in with the desert clays and talc that the Egyptian potters were using. In any event, Egyptian paste was in use before 5,000 BCE.
From that time through to Roman occupation of Egypt, Egyptian paste was used extensively. Main products were beads, charms, and special objects.
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How Egyptian Paste Works
Egyptian paste is a ceramic body (called that because it may or may not contain any actual clay) that includes soluble sodium carbonate. As the paste dries, the sodium carbonate migrates through the body to the surface of the piece, pulled by the action of water moving out of the piece as it dries.
Colorants that are included in the paste are pulled along with the soluble sodium carbonate. Although different colors were used, the most common colorant was copper. The copper and sodium work together to produce a strong, lovely turquoise blue. Even though copper is the most recognized Egyptian paste colorant, other colorants can be used.
Characteristics of Egyptian Paste
Egyptian paste is very non-plastic; it is stiff and sticky if too much water is added. Although all hand building techniques can be used, Egyptian paste works best when formed or carved into simple shapes. It is well suited for use with press molds, as well.
During drying, pieces should be left untouched. This is because the glaze materials rise to the surface, becoming a very fragile, almost furry-looking, coating. The slower a piece dries, the longer the sodium has to get to the surface. Therefore, slow drying helps achieve the best glaze coating possible.
Egyptian paste is a low-fire body and should generally be fired between 1562° and 1742°F (850°C - 950°C). It is not bisqued first, since the glazing materials are already on the piece.
Egyptian Paste Recipes
Egyptian paste recipe is generally, about 60% of the body will be non-plastic material; there will be at least 10% of a sodium-bearing material such as soda ash, bicarbonate of soda, or borax; and there may be up to 20% clay.
Basic Egyptian Paste