Chemical Properties of Egg Tempera
Art is traditionally viewed as a creative process far removed from science. However, beyond the imaginative efforts that contribute to the creation of a work of art are the physical materials that are used as the medium. While science is not an essential part of the thought and design process, an understanding of the chemical properties of different art media is integral to creating a work of art that will not only match the artist’s vision but will also stand the test of time. One such medium to be investigated is egg tempera, a specific type of paint. The use of this technique dates back to Ancient times, and is one of the oldest known painting techniques.
The chemical properties of tempera paint can be explained once the process of its production is understood. Egg tempera is made by mixing pigments with an egg yolk binder. This mixture is then thinned with water, acting as the solvent. Knowing the solvent contributes information about the polarity of this painting medium; because water is a polar substance, egg yolk must also be polar in order for the two to be able to combine. While this is true, egg yolk is unusual in this regard, due to the fact that it is itself essentially an oily emulsion. Typically, one would expect such a substance to be nonpolar and to repel water, but the presence of lecithin means that there are special properties associated with egg yolks that result qain the formation of an emulsion with the egg yolk in the water (Church 87-88). So while an egg yolk is not necessarily soluble in water, in the case of egg tempera, it behaves as though it is. Other information can also be taken from the properties stated above. One important distinction is that the paint is formed through hydrogen bonding, as egg yolk is water-soluble, and that it dries primarily through a process of evaporation. Based on this fact, the solvent of water is what makes the paint workable, as it prevents the hydrogen...
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