Watercolor painting to paints that use water-soluble, complex carbohydrates as a binder. Originally (in the 16th to 18th centuries), watercolor binders were sugars and/or hide glues, but since the 19th century, the preferred binder is natural gum arabic, with glycerin and/or honey as additives to improve plasticity and solubility of the binder, and with other chemicals added to improve product shelf life. The term "bodycolor" refers to paint that is opaque rather than transparent. It usually refers to opaque watercolor, known as gouache. Modern acrylic paints use a acrylic resin dispersion as a binder. Watercolor painters before the turn of the 18th
Gum printing copies. Gum printing Gum printing is a way of making photographic reproductions without the use of silver halides. The process uses salts of dichromate in common with a number of other related processes such as sun printing. When mixtures of mucilaginous, protein-containing materials together with soluble salts of dichromate are exposed to ultraviolet light, the protein content becomes tanned and resistant to solution in water. The untanned material can be washed away in warm water leaving a hardened, tanned protein negative. For gum printing a solution of gum arabic is mixed with either potassium or ammonium dichromate. The higher the