Gum resins, such as gal-banum, ammoniacum, myrrh, asafetida, and scammony, contain gummy matter, as well as resin insoluble in water, so that the addition of an emulsifier is not absolutely required. It is generally only necessary to rub down the gum resin to as fine a powder as possible, and emulsify with water. In warm weather this is not always practicable, as the gum resin is too soft. It is then best to put it into a mixture-mortar in small pieces, sprinkle it with water, and put the mortar with the pestle in a moderately warm place until the substance has become of the consistence of honey. To each gramme of the gum resin are added 1 drop of almond oil and 3 drops of mucilage of acacia, and then, by the gradual addition of warm water and vigorous working with the pestle, a good emulsion will be obtained.

Generally gum acacia or yolk of egg is ordered with a gum resin to emulsify it better. If either of these is used the gum resin should be in very fine powder. One part of gum acacia to 2 parts of gum resin, or one yolk of egg to 20 grammes of gum resin, is the usual proportion. If the gum resin cannot be powdered it is softened by warming, as explained, but with yolk of egg the temperature must not exceed 6o° C.