Gouache to acrylic or oil paints in that it is normally used in an opaque painting style and it can form a superficial layer. Many manufacturers of watercolor paints also produce gouache and the two can easily be used together. Gouache paint is similar to watercolor, however modified to make it opaque. Just as in watercolor, the binding agent has traditionally been gum arabic but since the late nineteenth century cheaper varieties use yellow dextrin. When the paint is sold as a paste, e.g. in tubes, the dextrin has usually been mixed with an equal volume of water. To improve the
Hand-colouring of photographs finish. Before the paint can be applied, the surface of the print must be primed so that the colours are not repelled. This often includes prepping the print with a thin coating of shellac, then adding grit before colouring. Watercolour paint used in photographic hand-colouring consists of four ingredients: pigments (natural or synthetic), a binder (traditionally arabic gum), additives to improve plasticity (such as glycerine), and a solvent to dilute the paint (i.e. water) that evaporates when the paint dries. The paint is typically applied to prints using a soft brush. Watercolours often "leave a darker edge of color at