Wikipedia
Glue-size is a painting technique in which pigment is bound ( sized) to cloth (usually linen) with hide glue, and typically the unvarnished cloth was then fixed to the frame using the same glue. Glue-size is also known as distemper, though the term " distemper" is applied variously to different techniques. Glue-size was used because hide glue was a popular binding medium in the 15th century, particularly among artists of the Early Netherlandish period, who used it as an inexpensive alternative to oil. Although a large number of works using this medium were produced, few survive today, mainly because of the high perishability of linen cloth and the solubility of hide glue. Well-known and relatively well-preserved — though substantially damaged — the most notable examples include Quentin Matsys' Virgin and Child with Saints Barbara and Catherine (c. 1515-25) and Dirk Bouts' Entombment (c. 1440-55). In German the technique is known as Tüchleinfarben, meaning “small cloth colours”, or Tüchlein, derived from the German words Tüch and Lein ("fabric" and "flax").