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
Narva Oil Plant from the power plants and the separate subsidiary of Eesti Energia was established. The retorting plant consists of two modified Galoter type solid heat carrier retorts (Enefit retort)—both processing 125 tonnes per hour of oil shale. Main products are fuel grade shale oil, raw material for bitumen and antiseptics. The designed annual capacity of the plant is 220,000 tons of shale oil and 60 million cubic meters of retort gas. In May 2009, Eesti Energia announced that it plans to build a new shale oil plant adjacent to the existing plant with processing capacity of 2.26 million tonnes of oil