Oil paint very slowly, darken, and crack, unlike mastic and wax (the latter of which was used in encaustic painting). Greek writers such as Aetius Amidenus recorded recipes involving the use of oils for drying, such as walnut, poppy, hempseed, pine nut, castor, and linseed. When thickened, the oils became resinous and could be used as varnish to seal and protect paintings from water. Additionally, when yellow pigment was added to oil, it could be spread over tin foil as a less expensive alternative to gold leaf. Early Christian monks maintained these records and used the techniques in their own artworks. Theophilus
Essential oil Essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (defined as "the tendency of a substance to vaporize") aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetherolea, or simply as the oil of the plant from which they were extracted, such as oil of clove. An essential oil is "essential" in the sense that it contains the "essence of" the plant's fragrance—the characteristic fragrance of the plant from which it is derived. The term essential used here does not mean indispensable as with the terms essential amino acid or essential fatty