The varnish trade usually refers to the natural resins as gums. In strict terminology, however, the gums are related to the sugars and carbohydrates. They are soluble in water, forming viscous solutions, and insoluble in drying oils and organic solvents. On heating, they decompose completely with out melting. In contradistinction, the resins are insoluble in water, more or less soluble in organic substances and vegetable oils, and are chemically related to the terpenes or the essential oils. On heating the resins melt with the distillation of volatile oils terpenic in nature. The residue, termed run gum or resin by the varnish maker, is soluble in hot vegetable oils. Some of the softer resins are directly soluble in solvents or oils, but in all cases are totally insoluble in water.