Update: If you want to know the best whiting I’ve tried so far, it’s marble dust. It’s cheap, hard, somewhat absorbent, but not too absorbent.
It can also be mixed into paint to make the paint go further and last longer, if you’re on a budget. You’d be surprised at how much you can mix into oil paint before the marble dust actually tints the color. In water media, it indeed tints quickly and can even be used as a cheap white paint.
I’ve been reading like mad about gesso. I think I love gesso. I’ve jotted down what I’ve read. I only hope that what I’ve read is factual, not a lot of painters’ myths. 🙂
My notes about size and gesso:
Size: a glue used to seal the pores of the painting support, in order to isolate it from the paint and vice versa.
For example, the lignins and acids in wood would eventually leach upward into the painting, yellowing the paint, without being sealed off from the paint. Inversely, the paint might all be absorbed downward into the support. Also, the oil in oil paint could rot both fabric and paper. So, we want something penetrating into the fibers of the painting support, surrounding and isolating them.
The traditional size is rabbit skin glue. (now, if it were squirrel skin glue, I might be tempted to make my own. Darn squirrels are eating the peaches off the tree…that reminded me to locate the pellet gun).
Gesso / ground: a base for the paint. You apply it to the painting support: canvas, board, etc. It gives the paint something to grip to. So, it is somewhat absorbent. However, if the ground is too absorbent, a diluted varnish might be needed over it.
Gesso is also chosen for a desired painting surface: smooth or textured. Some gesso can even be used as modeling paste (cool, I could sculpt mountains into a painting). Gesso can be mixed with paint or pigment and used as a painting medium, if desired.
Acrylic gesso (no need for size) can be used with acrylic and oil paints, but an oil-based gesso cannot be used as a ground for acrylic paint. Also, acrylic gesso is incompatible with egg tempera.
For homemade gesso, you can mix a glue and a whiting/filler, with sufficient water to spreadable consistency. The whiting can be gritty, to give texture, or a fine powder, for smoothness that still has ‘tooth’ (grip). Gypsum absorbs the initial layer of paint evenly, for an even paint film, so has been preferred for centuries.
casein + alkali (borax preferred)
PVA glue (Elmer’s glue)
methyl cellulose adhesive? (I doubt it)
talc/baby powder (soft)
baking soda (too absorbent!)
(addition of titanium is optional: only for a brilliant white)
For casein glue, I decided to use the recipe from this site http://www.askmaurice.org/casein.html:
1 Enameled or Pyrex pot (non-metallic)
1 qt skim milk
6 oz vinegar
4 oz distilled water (tap water is susceptible to bacteria mold growth)
1 oz borax (can be substituted with baking soda, quick lime, aqua ammonia or ammonium carbonate)
The casein protein in milk has historically been used as glue. Addition of an alkali makes it glutinous. Borax as the alkali makes a PH neutral glue, suitable for all pigments. The borax acts as a preservative too (not eternal). This glue is an emulsifier – will take oil.
The casein glue can be used as size, in gesso, in milk paint and as a fixative. It’s strong, is somewhat absorbent. It dries brittle, so use is limited to rigid supports. It’s water soluble until dry (another way of saying that: it’s insoluble when dry!).
The making of PVA gesso was simple. I squirted Elmer’s glue into a container, added the same amount of water, then stirred in baby powder. Later I realized I prefer corn starch. It’s smoother. Oh, I added a little baking soda to the Elmer’s glue/water mix, to neutralize the slight acidity of the glue. When the gesso was dry, I had to sand it smooth with fine sandpaper.
My preference is the casein glue + corn starch gesso, for a smooth, flat surface ground, which can take any paint. I have no idea whether corn starch is stable, archival-quality. My purpose was to slap some homemade gesso onto corrugated cardboard and make practice paintings. But I’m so impressed with the homemade gessoes and the ability to paint on all sorts of surfaces, that I’m going to look into it more.
Update: I’ve learned that strong sunlight cracks gesso. 🙁
For more on gesso, read the section Grounds, starting page 18, in the casein booklet: http://cindymckee.com/librejo/Casein-advice.pdf