In following out instructions of former times, it is important to remember that the character and nomenclature of many materials have undergone change. This is useful for the purpose of giving an account of the methods of the artist's craft, in order to gain control over manipulations, and convey intentions properly, insuring the permanence of results. To recognize old controversies or repetitions of long-buried disputes, such as the theory that the Masters had some closely guarded secrets, may improve the understanding of the general principles of the technically building up a picture. See also AATA 18-1441.