"No authentic Greek paintings of the classical period are known to exist."
pg 19

"Examination of decayed canvases of great age, of early American canvases, and also of those of 1890-1910, ... shows almost invariably that the portions of a canvas over the stretcher bars and crosspieces are in a better state of preservation than the rest of the picture... (This) shows the efficacy of an independent layer of material back of the canvas, even when the protection is only partial."
pg 260

Ralph Meyer's Artist's Handbook
Faber (third edition)