Pigment Making Preparation of Egg Tempera and Panel Preparation Theresa Panagou

Pigment Making, Preparation of Egg Tempera, and Panel Preparation
Edited by M. Santala, Conservator

Basic Grinding:
Pigment making is usually a straight forward process. The method used depends the character of the mineral to be refined and the desired fineness of the pigment. If the mineral is crumbly, like azurite, it is best to break it in to very small pebbles in a strong metal mortar and then grind it in a hard stone mortar. Please note that one may use the metal mortar to break up the mineral but do not grind it in one, as the mineral may be dulled from picking up tarnish from the mortar. After grinding the pigment to a powder, the grades of pigment may be separated out with water (see section on Levigation below). If a mineral is hard but not glassy, and is compact but with a soft structure, like amorphous hematite, a metal file will produce a finely ground pigment. If the mineral is hard and glassy, like jewelry grade malachite, the same method as for crumbly minerals may be used.

Levigation:
After grinding a mineral into powder the fine pigment particles may be separated from the coarse one by a process called levigation. To perform this process, pour water into the stone mortar containing the powdered mineral, stir the powdered materials and water quickly and thoroughly, and pour the water out into a shallow dish without letting the bulk of the pigment pour out of the mortar. The finer pigments are temporarily suspended in the water when it is stirred, and will flow out with the water. Left to sit, the pigment will settle to the bottom of the dish. Pour out as much of the clear water from as possible from the dish once the pigment has settled. Let the remainder of the water evaporate, scrape the pigment off the dish, and store pigment in glass jars. After cleaning the ground minerals in the mortar with water a few times, the water will remain clear, with sandier, heavier particles left at the bottom of the mortar. Continue the process of grinding/levigating this until it is all fine pigment, or until you are left with sandy particle that resist further processing. Some minerals, like azurite and malachite, will have a brightly colored, but grainy and somewhat hard to use sand left over after processing. When grinding pigment for egg tempera, the degree of fineness required depends on the texture you want. If grinding pigments for handmade oils or watercolors, the pigment should be very fine, and further grinding with stone and/or glass muller should be done after levigation, to further refine the pigment.

Egg Tempera:
To make a very stable egg tempera base, separate out the yolk of one egg without breaking the yolk sack. When most of the egg white has been removed from the yolk, roll the yolk into the palm of one hand, and then carefully to the other. The whole surface of the egg should touch dry skin, taking more white off. After each rolling, dry the residual white off the hand with a paper towel or rag. Repeat the process until the egg yolk is practically dry. (One may also simply roll the egg yolk on a paper towel to remove the white, but it may occasionally stick to the towel and break.) Once dry, either gently pick up the yolk (like picking up a cat by the back of the neck) or separate the fingers at the middle and ring finger, and roll the egg over this separation. Over a very small dish or cup, pierce the yolk sack, and drain the yolk into the container, taking care not to drop the yolk sack into the yolk. When the sack is emptied, discard. Add approximately one teaspoon water to the yolk, more or less depending on it's size, and mix very well. Pigment can now be added to the egg, mixed, and used directly. Egg tempera does not keep for very long. It is best to mix what you will use when you will use it. The mixture is usually less than half pigment to more than half of the egg/water mixture. Mixtures with a lower proportion of pigment are incredibly transparent, and not muddy. It is best not to mix different pigments together directly into the egg, but rather mix colors through a series of layers or glazes. Egg tempera is dry to the touch about ten seconds to 2 minutes after it is applied, but isn't complete dry for about a year. No more than four layers should be applied in one day, and less is better. The paint can crack, and, if applied to a less than perfect surface, flake off, if too many layers are applied at once. The medium requires drying in sunlight, or at least daylight to properly set. The sunlight changes the chemistry of the egg. It is best if work from one day is allowed to rest and set in the sun all of the next day or longer.

Panel/Ground:
Tempera should be applied onto a smooth, ridged, bright white surface. If the surface is flexible (like stretched canvas), the paint may flake off if the canvas is flexed or bowed. The best prepared surface is a high-grade ply wood (like birch ply), sized with and animal hide glue, then covered in a light natural fabric, like linen (I use a light muslin) soaked in the same glue, and then gessoed/sanded several times each. It is best to use a traditional gesso, consisting of powdered marble or another chemically neutral fine white substance (DO NOT USE LIME- it is not chemically compatible with all colors, especially copper carbonates like azurite/malachite, and will blacken them), mixed with an archival animal hide glue, preferably rabbit. I personally prefer plain plaster of paris mixed with the hide glue, but a conservator friend of mine has lectured me against it. It is preferable to apply multiple (at least eight) thin coats of gesso rather than fewer thicker ones. When completely dry, the gesso is sanded with progressively finer grades of sand paper/cloth, until the surface shines. The smoother the surface, the better the tempera seems to stick (think of how hard it is to clean a glazed, breakfast dish that has egg yolk dried on it). As mentioned, egg tempera is almost perfectly transparent/translucent. If the pigment used is fine and not very opaque (like charcoal), and the ground is bright white and it has been sanded until it shines, light hitting the painting will pass though the paint layers, bounce off the white ground, and back though the paint, producing an incredibly vibrant effect.

Minerals listed above:

azurite - lapis colored copper carbonate producing a color from a finely powdered, sky blue to a coarse, brilliant ultramarine sand.

amorphous hematite - iron oxide, very good cool orange-y-red, which stains everything- therefore not kind or clean on stone mortars.

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