solution is concentrated. Modern alternatives to bone char include activated carbon and ion-exchange resins. Black pigment Bone char is also used as a black pigment for artist's paint, printmaking, calligraphic and drawing inks as well as other artistic applications because of its deepness of color and excellent tinting strength. Bone black and ivory black are artists' pigments which have been in use since historic times—by both old masters like Rembrandt and Velázquez and more modern painters such as Manet and Picasso. The black dresses and high hats of the gentlemen in Manet's Music in the Tuileries are painted in ivory black. Ivory black was formerly made by grinding charred ivory in oil. Nowadays ivory black is considered a synonym for bone black. Actual ivory is no longer used because of the expense and because animals that are natural sources of ivory are subject to international control as endangered species. Niche uses It is used to refine crude oil in the production of petroleum jelly. In the 18th and 19th century, bone char mixed with tallow or wax (or both) were used by soldiers in the field to impregnate military leather equipment, both to increase its lifespan and as the simplest way to obtain pigment for black leatherwares. Military and civilians used it as shoe polish and preservative, including on shoes with the "rough" side out. In period reference materials, it is referred to as "black ball". The ESA-NASA Solar Orbiter satellite uses a refined form of bone char which is applied to its titanium heatshield. This protects it against the glare and heat of the sun. The coating was developed by Irish company Enbio and uses its 'CoBlast' technique, originally developed to coat titanium medical implants. In popular culture The production of bone char was featured on the Discovery Channel's TV series Dirty Jobs, on episode 24 of season 4, "Bone Black", originally broadcast on 9 February 2010. Human bone char, referred to as "bone charcoal", is mentioned in Thomas Pynchon's novel The Crying of Lot 49. The bones come from US soldiers who died in combat during WWII and were buried in a lake in Italy, and the char is used for filters in cigarettes. Human bone char, referred to as "bone charcoal", is mentioned in Jaroslav Hašek's novel The Good Soldier Švejk. The work contains a reference to soldiers not dying in vain because their bones will be