I'm looking at two portraits of the same man dating from the mid-to-late 1870s. They differ in that the subject is obviously younger in one. They are alike in that they're 16x20 and it appears that he is wearing the same clothes in both - except in one the coat buttons are black and white in the other. Have been told that portrait photographers of the period would "draw" the clothing for their subjects - thus explaining the apparent sameness in the clothing. Does anyone know for sure if that was a common technique? Is there a good reference book on early portrait techniques?