This is a summary of the methods which a restorer may use to distinguish later additions. These are grouped in 4 sections: (1) historical and iconographical criteria, (2) differences visible in ordinary light to the naked eye, or under low magnification, (3) differences revealed by special equip ment, (4) differences revealed by cleaning. Such a summary, however complete, can do no more than aid a restorer, who relies much more on his skill and experience than on the nature of the methods he uses.