PW21

A common extender/filler in oil paints. A longer discussion of this pigment can be found under the related pigment code, PW22. These are closely related pigment numbers, however, the artificial kind (PW21) is said to have greater covering ability and has a finer consistency. Barium sulfate has different roles in water-based media (it is used in gouache) than oil-based media. In oil it has a low oil absorption, but is also linked to yellowing. In titanium white, It can actually contribute to the breakdown of the binder in oils due to light exposure and lead to problems like chalking, according to George O’Hanlon via this article. Seymour has an interesting discussion in the Artists’ Handbook of its complex relationship to opacity, as well as its weight, which can mislead artists into thinking a given tube of paint has a higher pigment load. This may particularly be a problem in more expensive colors where artists are looking for high pigmentation but can only go off of the feel of a paint tube to judge the quality. It is also used as a base in lake pigments.