The double boiler is an indirect way to evenly heat oily or waxy mixtures which are flammable. It will keep the oil from getting too hot too fast and becoming a fire hazzard. If you don't have access to a double boiler, it can be improvised by floating a stainless steel pan in a pot that is slightly larger than the steel pan. NEVER HEAT oil directly on a heat source without some kind of double boiler. Indeed, if you have an open flame gas stove, it would be safer--as it is with candle-making--to use a plug-in electric stove top. Hot oil, like hot wax, should not be heated on an open flame.
I should clarify that the oil used to make an oil-based infusion should always be some sort of natural plant oil, such as olive oil, almond oil, sesame seed oil, or another salad oil. NEVER use petroleum-based oils, such as mineral oil. Different types of oils respond differently to head. Petroleum-based oils can be extremely hazzardous when heated. They may react in unforeseen ways with ingredients, even when mixed cold. They may also act as a skin irritant. Oils such as olive, almond, and sasame have been used for thousands of years.
I have never made an oil-based infusion by this method. I have more practical experience with oil infusions that do not require heating. However, according to Judika Illes, it is one way to get an oil infused with official vervain (Verbena Officinalis) instead of lemon verbenna (Lippia Citriodora).
Disclaimer: I have tried to make clear any possible hazzards involved in the mixing of oils. Any visitor to this website who disregards hazzards or common sense involving sources and fire surely invites the wrath of fire elementals and others. The creators of this website accept no liability if any oils do not have their desired affect or result in adverse affects.
Italian Rose Oil