Cake and moist water colours are made by grinding the dry pigments in a mill with gum water and a little glycerine or honey to prevent them becoming too brittle; the pasty material is rolled out and cut into squares, partly dried, and then pressed in moulds or placed in tins. For the moist colours more gum water is used than for the cakes. The gum water is made by dissolving purest gum arabic in twice its weight of water and straining through muslin, then adding a little glycerine and a few drops of oil of cloves. Very little glycerine must be vised or the colours will tend to absorb moisture from the air and fade or become bad.