My husband, who is an oil painter, talks a lot about mediums, how to use them and the mystery surrounding them. Watercolor has its share, some with more practical uses than others.
I like using gum arabic. Gum arabic is the binder in watercolor paints, albeit some brands have variations of this theme. It has a couple very good applications. For one, it will add a luster to your work. Some beginning watercolorists may be disappointed with watercolor, that it seems lifeless after the paint as dried. Gum arabic can add this bit of gloss.
There is a long history of its use with Victorian watercolorists. Gum arabic and bodycolor, or gouache, were mixed with watercolors and used to make watercolor paintings resemble oil paintings and get the prices that oil paintings were fetching. Only fair it would seem, with the medium many consider the most difficult. The Victorian watercolorists would mix it with their paint or use it after the painting was done to "heighten" certain areas. Of course, this is with a very gentle hand, so as not to upset the painting. Now before purists cry "foul", this was a point of contention at the time, but there’s no denying that the paintings of this era are absolutely stunning. Just check out some of the work of William Henry Hunt or John Fredrick Lewis.
You can use it in several ways. I like to wet an area with a gum arabic/water solution if I want a bit of control over where the paint will go, perhaps to control the amount of blending in a variegated wash. You need only a drop or two with your water to accomplish this. I’m talking about maybe a quarter cup of water and the gum arabic. I mix up just a small bit to use when I need it. Too much and the paint won’t move at all and the risk of the paint cracking increases. Just pre-wet the area and drop your paints in.
Painted areas where gum arabic has played a role can lift easier. This can be good or bad, depending upon your painting. Adding it to your paints and then misting a painted area with water and blotting the area can lend a nice texture to say rocks or foliage. The misting gives the irregular pattern and the gum arabic makes the paint easy to lift.