Prepared canvas, painted with white lead, is so extensively used that some means of knowing how to minimise its injurious reactions is useful to know. One good method is to paint the back of the prepared canvas with a coat of zinc white in linseed oil or else in white lead, over which another coat of zinc white is laid.,...,The practice adopted by some painters of backing their canvasses with prepared canvas reversed, cannot claim to be very effectual in preventing the darkening of the painting ground by absorption of noxious gases; but an extra backing of canvas is a precaution to be recommended against accidental damages.,,