We generally think of paint as complex and somewhat mysterious in composition, but it is, quite simply, a combination of pigments (that provide color), fillers (that determine opacity and coverage), and some type of binder or glue (that adheres to a wall). It’s actually pretty easy to make paint from casein, a milk protein, or starch from grain flour. However, you’ll need to be willing to experiment with the amounts of ingredients you use. Your results may not be perfect at first, but with some practice, you can mix up nontoxic, homemade paints in a flash.
Making Paint from Clay and Starch
The paints made in many traditional cultures used flour (rice, rye, potato) to create a starchy binder with clay as a filler and pigment. In the southwestern United States this traditional type of paint is referred to as an “alis” from the Spanish word alisar, which means “to make smooth.”
Starch paints with clay can be applied over a wide range of surfaces, but they’re generally incompatible with joint compound. They’re not water resistant, so they’re most appropriate for interior use. However, they can be coated with a glaze of linseed oil and citrus thinner, casein emulsion, or a silicate primer for additional protection. Use starch/clay paints shortly after you make them, as they’ll spoil. They can be refrigerated for a short time, but doing so results in a gradual loss in binding power.
About Clay Paint Ingredients
• Powdered clays and fillers can be purchased from suppliers of ceramic materials. Colors typically include white, beige, terra-cotta, and red.
• Local colored clays can be collected and sifted using a 30- to 40-mesh screen (or a window screen).
• Pigments and colored mica are available through natural paint suppliers.
• Larger quantities of mica are available from PT Hutchins.
1 part wheat, rice, rye, or potato flour
2 parts cold water
1-1/2 parts boiling water
1 part powdered clay
1/2 part inert powder filler (options: mica flakes and powder, chalk, powdered marble or silica, 60- to 80-grit sand for rougher surfaces)
Small amount of finely chopped straw, for visual effect (optional)
1. In a bowl or container, mix flour and cold water.
2. Meanwhile, in a large pot, heat water. When it boils, add the flour water. Turn heat to low and stir until thick paste develops.
3. Dilute the paste, using a ratio of 1 part paste to 2 parts water.
4. Add the clay and filler into the pot with the diluted paste; mix together. (The filler prevents the paint from peeling and cracking; however, no filler is needed if you want to create a paint with a thin, wash-like consistency.) The paint can be quite thick, as long as it can be spread with a brush.
5. To apply, brush on paint, then smooth out brush marks with a damp tile sponge or a clean, damp brush. When the paint is still moist and leather hard, a clean, damp sponge can be used to remove a layer of film and reveal the mica or straw.
Making Paint from Milk
Casein paint, also known as milk paint, was traditionally prepared from the curds of nonfat milk, also referred to as “quark” in Germany. Casein is a protein component of milk that can also be purchased in powder form; one part casein powder equals six to eight parts curds. When combined with an alkali such as lime or borax, casein develops binding ability. (Lime is more water resistant, but borax is particularly useful for glazes or emulsions.)
When making this paint, pay careful attention to the proportions. The ratio of casein binder to fillers, pigments, and water must be kept in balance. If the casein is too concentrated, the paint will peel or crack. If insufficient casein or too much water is added, the paint will dust.
Casein paints are intended for indoor use and should be avoided in constantly humid areas such as bathrooms, kitchens, basements, root cellars, or laundry areas. The best surfaces include porous wood, earth and lime plaster, stone, and paper. Don’t use on smoothly troweled plaster, latex, gypsum, or plastic. The surface should be thoroughly dry, and it’s always advisable to test the paint before applying.
CASEIN PAINT FROM CURDS AND LIME PUTTY
Casein paints are most often prepared by measuring the ingredients by weight, so you’ll need a simple digital kitchen scale to make your own. You may need to adjust for consistency by adding more water or filler. The paint is best used the same day it’s mixed because, with time, its binding power diminishes and the milk protein can become moldy.
By weight:Approximately 20% curds (quark)*
Approximately 5% lime putty*
75% filler and pigment combined [filler options: chalk (most commonly used), powdered marble, powdered mica, a small amount of kaolin clay, or combination of these]
1/3 liter water for every 2.2 pounds of filler
* These proportions (by volume) give similar results: 1 part casein/lime binder, 3 parts filler/pigment, 1 part water.
To make curds (quark):
1. Leave a carton or jug of nonfat milk in a warm place for several days to sour. (To speed up the souring process, gradually add several drops of lemon juice to the milk until you begin to see it curdle. Adding lemon juice makes the curds become acidic, so wash them thoroughly.)
2. Hang the curds in a linen cloth or cheesecloth to drain off excess whey.
To make lime putty:
1. Use Type S lime (dry powder), available in large bags at building-supply stores. You’ll need less than a cup for a gallon of paint, but you can store lime indefinitely for use in plaster or other paint projects.
2. In a container, gradually add water to the dry powder until a toothpaste-like consistency is achieved.
Making the Paint:
1. Combine lime putty and curds using a blender or an electric drill with a paint-mixing bit. Add a little water if needed. Strain the mix to remove any lumps and wash the blender immediately.
2. On a surface that can be easily cleaned, mash the pigments with a rolling pin. Add ground pigment to the casein/lime/water mixture. Add remaining liquid and filler.
Pigment note: Smaller amounts of pigment with higher percentages of fillers make less intense colors. For a wash rather than a solid paint, reduce the amount of combined filler/pigment. Add the additional water.
To apply: Test samples and adjust as needed. The paint may need additional water to spread easily, additional binder if it dusts, or additional filler/pigment if it’s too thin.
Alternate Casein Paint Formulas
CASEIN PAINT FROM CURDS AND BORAX
75% combined filler (options: chalk, powdered marble or mica, combination of these)
1. In a small container, mix borax into hot water until dissolved. Let cool.
2. Place curds (see curd-making instructions) into a large container. Add the borax/water mixture and let sit for about 2 hours.
3. Add filler into container. Thin with water to the desired consistency. (Applying a couple of thin coats is better than one.)
CASEIN PAINT FROM POWDER AND LIME PUTTY
Yields slightly more than a quart
1/4 cup casein powder
2 to 3 cups water
1 tablespoon lime putty (or substitute 1 ounce borax)
If opaque paint is desired: Less than 2 cups chalk or powdered marble
1. Soak casein powder in a little more than 1 cup of water for several hours or overnight.
2. Combine lime putty (or borax) with the casein/water. Mix with an electric drill for several minutes. Add another cup or so of water.
3. Add chalk or powdered marble. Adjust water as needed.
The paint will appear somewhat transparent as it’s being applied, but it will become more opaque as it dries. Avoid the temptation to paint thick coats. It’s helpful to apply a priming coat of a weak casein solution, especially on porous plaster and stone surfaces.
Pigments that produce the most pleasing results typically come from natural mineral and plant sources. Pigments can be relatively harmless or highly toxic; it’s essential to know the difference. Companies that handle natural paint products most likely will supply only nontoxic pigments. Both Kremer Pigments in New York and Sinopia in San Francisco classify pigments according to whether or not they pose any health risk.