Tempera (not tempura)

Here is the link to the video we watched about tempera.

Tempera
     Tempera, also known as egg tempera, is a permanent, fast-drying painting medium consisting of colored pigment mixed with a water-soluble binder medium (usually a glutinous material such as egg yolk or some other size). Tempera also refers to the paintings done in this medium. Tempera paintings are very long lasting, and examples from the 1st centuries AD still exist. Egg tempera was a primary method of painting until after 1500 when it was superseded by the invention of oil painting. A paint consisting of pigment and glue size commonly used in the United States as poster paint is also often referred to as "tempera paint," although the binders and sizes in this paint are different from traditional tempera paint.

History 
     Tempera painting has been found on early Egyptians sarcophagi decorations. A related technique has been used also in ancient and early medieval paintings found in several caves and rock-cut temples of India. High-quality art with the help of tempera was created in Bagh Caves between the late 4th and 10th centuries AD and in the 7th century AD in Ravan Chhaya rock shelter, Orissa. 
    The art technique was known from the classical world, where it appears to have taken over from encaustic painting and was the main medium used for panel painting and illuminated manuscripts in the Byzantine world and Medieval and Early renaissance Europe. Tempera painting was the primary panel painting medium for nearly every painter in the European Medieval and Early renaissance period up to 1500. For example, every surviving panel painting by Michelangelo is egg tempera.
     Oil paint, which may have originated in Afghanistan between the 5th and 9th centuries and migrated westward in the Middle Ages eventually superseded tempera. Oil replaced tempera as the principal medium used for creating artworks during the 15th century in Early Netherlandish painting in northern Europe. Around 1500, oil paint replaced tempera in Italy. In the 19th and 20th centuries, there were intermittent revivals of tempera technique in Western art, among the Pre-Raphaelites, Social Realists, and others. Tempera painting continues to be used in Greece and Russia where it is the required medium for Orthodox icons.

Technique
     Tempera is traditionally created by hand-grinding dry powdered pigments into a binding agent or medium, such as egg, glue, honey, water, milk (in the form of casein) and a variety of plant gums.
     Tempera painting starts with placing a small amount of the powdered pigment onto a palette, dish or bowl and adding about an equal volume of the binder and mixing. Some pigments require slightly more binder, some require less. A few drops of distilled water are added; then the binder (egg emulsion) is added in small increments to the desired transparency. The more egg emulsion, the more transparent the paint.

Egg tempera
     The most common form of classical tempera painting is "egg tempera." For this form most often only the contents of the egg yolk is used. The white of the egg and the membrane of the yolk are discarded (the membrane of the yolk is dangled over a receptacle and punctured to drain off the liquid inside). Egg yolk is never used by itself with pigment; it dries almost immediately and crackles when it is dry. Some agent is always added, in variable proportions. One recipe calls for vinegar (1:1 proportion to egg yolk by volume); other recipes suggest white wine (1 part yolk, 2 parts wine). Some schools of egg tempera use various mixtures of egg yolk and water.When used to paint icons on church walls, liquid myrrh is sometimes added to the mixture to give the paint a pleasing odor, particularly as worshipers may find the egg tempera somewhat pungent for quite some time after completion.
     The paint mixture has to be constantly adjusted to maintain a balance between a "greasy" and "watery" consistency by adjusting the amount of water and yolk. As tempera dries, the artist will add more water to preserve the consistency and to balance the thickening of the yolk on contact with air. Once prepared, the paint cannot be stored. Egg tempera is water-resistant, but not waterproof.
     Different preparations use the egg white or the whole egg for different effect. Other additives such as oil and wax emulsions can modify the medium. Egg tempera is not a flexible paint and requires stiff boards; painting on canvas will cause crackle and pieces of paint to fall off.

Tempera grassa
     Adding oil in no more than a 1:1 ratio with the egg yolk by volume produces a water soluble medium with many of the color effects of oil paint, although it cannot be painted thickly.

Pigments
     Some of the pigments used by medieval painters, such as cinnabar (contains mercury), orpiment (contains arsenic), or lead white (contains lead) are highly toxic. Most artists today use modern synthetic pigments, which are less toxic but have similar color properties to the older pigments. Even so, many (if not most) modern pigments are still dangerous unless certain precautions are taken; these include keeping pigments wet in storage to avoid breathing their dust.

Application
     Tempera paint dries rapidly. It is normally applied in thin, semi-opaque or transparent layers. Tempera painting allows for great precision when used with traditional techniques that require the application of numerous small brush strokes applied in a cross-hatching technique. When dry, it produces a smooth matte finish. Because it cannot be applied in thick layers as oil paints can, tempera paintings rarely have the deep color saturation that oil paintings can achieve. In this respect the colors of an unvarnished tempera painting resemble a pastel, although the color deepens if a varnish is applied. On the other hand, tempera colors do not change over time, whereas oil paints darken, yellow, and become transparent with age.

Ground
     Tempera adheres best to an absorbent ground that has a lower "oil" content than the tempera binder used (the traditional rule of thumb is "fat over lean" and never the other way around). The ground traditionally used is inflexible Italian gesso, and the substrate is usually rigid as well. Historically wood panels were used as the substrate, and more recently un-tempered masonite and modern composite boards have been employed. Heavy paper is also used.