can be described as "mixing paint". Tempera is made by hand or using a pestle and mortar by mixing dry powdered pigments with egg yolk and water. The most commonly used tempera is egg tempera. Egg yolk is an emulsion of oil-like substances and water, in which egg whites are dissolved. When the tempera dries, the water will firstly vaporise, after which the egg whites denature and can no longer be dissolved in water. The oil does not appear to undergo chemical changes during the drying process and simply keeps the paint layer flexible. Paintings made with tempera have born the test of time. To counteract deterioration of the tempera, vinegar is sometimes added to the emulsion. Oil was also sometimes mixed in and it is believed that this is how oil paint was discovered. Since the discovery of oil paint, tempera has lost a lot of ground. It was often used as the base for the painting. Tempera paint is quite dull, and only becomes glossy when a wax layer or varnish is applied to it. Tempera is applied to a white background made from chalk and/or plaster of Paris. Tempera dries quickly and is liable to deterioration. Therefore, the artist has to remix his paint each time. Many traditionally used pigments comprise minerals or metals, a few of which are extremely toxic; they contain, for example, mercury or arsenic. Nevertheless, from time to time tempera experiences a revival and is rediscovered by artists; the fresh colours in particular are extremely appealing.

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