transparent vellum
VELLUM rendered
transparent by any of several processes, some of
which date hack to medieval times (when vellum was
sometimes used in lieu of window glass). The most
common method of making vellum transparent seems
to have involved treating a wet (thin) skin with
fluid substances of high water-binding capacity,
such as egg white, gum arabic, animal glue or
size. before drying the skin on the stretching
frame. Other methods included smearing olive oil
or cedar wood oil over both sides of the skin. or
steeping the skin in very hot water for a brief
period of time. In the 18th century EDWARDS OF HALIFAX
patented a method (1785) which proved to be the
simplest of all the methods. He soaked ordinary
vellum in a weak solution of potassium carbonate
(pearl ash) and, stretching it tightly, placed the
skin under considerable pressure. (236 , 291 )