D B Clemons - Casein Sizing

Casein Size and Gesso:

I've adapted various recipes for making traditional gesso by substituting casein emulsion for the hide-glue. It's recommended to only be used on firm supports such as wood panels. I've read that it's more brittle over time than hide-glue, and more absorbent; although, tempering (mentioned below) helps prevent that. It's a bit easier to manage than hide-glue, I think, since it doesn't require constant heating. I've used this surface for both oil and casein paint, but casein paint doesn't need as many coats. The whole process takes about 4-5 days, not including final drying time, so doing several panels at once is a good idea.

You will need:
Casein binder (see "Articles" section)
White pigment (titanium, or titanium and zinc)
Whiting (calcium carbonate, chalk, marble dust, or gypsum)
Denatured alcohol
Distilled water
Cheesecloth for straining gesso
#300 & #2000 grit sandpaper
Alum (aluminum sulfate - optional)
Blond dewaxed Shellac (optional)
Wood stirring spoon/sticks & spatula for mixing pigment
Several bowls for mixing
Measuring cups and spoons

Making the Size:
Dilute the binder to a sizing liquid by a ratio of 1:10 (10 times the water) by volume*. One tablespoon as a unit makes about ½ cup or so. This should be plenty for about 2x2 ft. with two coats. It dissolves well if you set the container inside a larger bowl of hot (not boiling) water and stir gradually until it's all diluted. Apply two coats on all sides of the panel, and let it dry well for 2-3 days before adding gesso. You can also size with just shellac, and casein gesso adheres well to that surface also.

Making the Gesso:
Mix 1 part pigment and 3 parts whiting**. Mix a few drops of alcohol diluted in your sizing liquid (1:1) and add gradually to the powder until it mixes into putty. This helps the glue adhere to the powder better. Let this sit for at least 15 minutes.

Alum can strengthen the dried gesso and cause it to be more water resistant, or so I'm told. One teaspoon added in the dry mix above will do. It can usually be found in the spice section of a grocery store.Generally, I don't find this necessary.

Pour some of your sizing liquid (@1oz.) into a large bowl, and add a ball of the pigment putty. Keep adding more liquid or more putty until it gets to a creamy consistency, and you have enough for your needs. If it gets too thin, pour a little of that into another bowl and add more putty. It also shouldn't be too thick, but milky and opaque. Test its properties on a scrap surface. Stir it slowly until the mixture is blended.

Cover another bowl with cheesecloth and strain the gesso into it slowly. Stir the gesso with a clean spoon. Strain as much of the grit out as possible.

It's always better to make slightly more than you need. A ½ cup should be plenty for @ 1x1 ft. panel.

Apply the Gesso:
Start applying the gesso by stippling the brush (sponge brushes work well) in a rather thin amount across a small area. If you're leaving brushstrokes, it's too thick. Use short back and forth strokes in one direction, making sure there's no uncovered spots or bubbles. If the coat seems too "streaky" the gesso may not be thoroughly mixed.

Let this coat dry to touch, lightly sand with #300 sandpaper, and then dust off. I've tried accelerating that with a hair dryer, but it tends to cause cracks to appear, so I recommend being patient. Apply another coat in the same manner with brush marks going in an opposite direction. Six to eight coats make a thick, smooth surface. Panels that have a mix of dark and light grain patterns will need the most coats. Give a final sanding with the finer grit #2000 paper.

Tip: If you use a large cylinder, like a tall jar or large bowl, to hold your gesso, it's easier to remove excess from your brush by dragging it inside the container, rather than across the rim, which can add air bubbles.

For storage, a glass container with a lid works best, and a plastic wrap inside the lid helps keep out bacteria. The mixture keeps well in refrigeration for 4 to 6 months. The older it gets, the weaker the glue becomes. Warm it to room temperature before using.

Let the panel dry for at least one week before painting. If you've never used a traditional gesso panel before, I think you'll love the smooth feel. It's similar to slate or chalkboard; very nice.

Tempering with Shellac:
Tempering the final coat of gesso makes the surface less absorbent, plus it keeps the gesso from lifting off with the first layer of paint. You can do this with a single thin layer of bleached dewaxed shellac cut 1:1 with denatured alcohol. Dried shellac flakes are best to use, since the commercial pre-mixed type contains lubricants or waxes to extend the shelf life and add gloss which you don't need. Wait for the final coat to cure for one week before you cover it. The shellac layer should dry for at least an hour before you start painting.

Footnotes:
· This ratio of 1:10 varies for RSG sizing recipes I've found, sometimes as high as 1:14. Strong glue can cause small cracks to appear later, so if you see that happening, use a more diluted mixture next time.
· Remember, when handling pigment to use care not to breathe it in, and don't wash your hands or tools in the kitchen. The powder easily flies off everywhere.