Gum notes

I’m supposed to be doing other things; instead I’m organizing my notes about watercolor.

Gum: The sap from a tree. Gum arabic is the sap from the acacia tree and is the traditional gum used in making watercolor paints. Also, sap from cherry, peach, nectarine, apricot, plum and almond trees (the Prunus genus) can be used.
All these gums share the same natural polymer (arabinogalactan). A watercolor painting does not cure. When it’s dry, it’s dry!
In contrast, oil, casein and egg tempera paintings all polymerize as they dry, so can have long curing times. Even a thick acrylic painting, even though made with a synthetic polymer, has a significant curing time as the polymer particles coalesce.

Applied as a watery wash, a lot of the gum is absorbed into the pores of watercolor paper. That lack of a protective film probably reduces the lightfastness of pigments, which are left exposed to the full effects of light. Use of a varnish or UV-protective glazing over the painting will compensate for the lack of a paint film.

Since watercolor depends upon the dispersion of pigments across the painting surface, fine pigments are generally used.
Because of that, when making homemade watercolor paint, it’s advisable to use only pigments of a small particle size.
If you try to make watercolor paint with coarse pigments, you’ll be grinding until your arm hurts.

Making your own binder: If you gather the balls of gum from a Prunus tree, you’ll need to soak the balls in a lot of water for a couple days. All I can tell you about volume of water is that you’ll need to use a lot more water than gum arabic requires.
You want to be left with a syrupy solution, not a gel.
Strain that through a loosely woven cloth or fine screen, to strain out bits of bark and other impurities, as well as any remaining clumps of gum.
That is your binder. You can mix that with pigments/pigment paste. The proportion depends on how you want your paint to behave. Usually, add no more than 25% of the total. More gum gives more control as you paint. Less allows for more spread of the paint over the surface, and more possible blooming.

The addition of sugar water (sugar dissolved in an equal amount of hot water) or honey water (equal amounts) to your binder will help the brushability and make it a little more transparent. You can add 20% by total volume to your binder.

Gouache is made by adding whiting when you grind paint. You can also use coarser pigments. Use a little more binder than for transparent watercolor.

The gums are emulsifiers, so if you want to experiment with temperas made by the addition of oils or waxes, go ahead!

Tip: Soft or softened water is a good wetting agent for watercolor. Minerals in hard water inhibit the spread of the paint. You can use distilled water or catch rainwater.

to be continued