"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