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 Narva Oil Plant Narva Oil Plant (), a subsidiary of Eesti Energia, is a producer of shale oil from oil shale. It operates a commercial scale shale oil retorting plant, located in Auvere near Narva, Estonia. The oil shale retorting plant (the UTT-3000 refinery) was built in the late 1970s next to the Eesti Power Plant to provide shale oil as a start-up fuel for the power plants. The plant was commissioned in 1980. Since the beginning of the 1990s, the oil plant operated as a part of the Narva Power Plants. In September 2007, the oil plant was separated