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
User-generated content based on user-generated content, including Wikipedia (2001) and Flickr (2004). The BBC set up a user generated content team as a pilot in April 2005 with 3 staff. In the wake of the 7 July 2005 London bombings and the Buncefield oil depot fire, the team was made permanent and was expanded, reflecting the arrival in the mainstream of the citizen journalist. After the Buncefield disaster the BBC received over 5,000 photos from viewers. The BBC does not normally pay for content generated by its viewers. In 2006 CNN launched CNN iReport, a project designed to bring user generated news