Well, I googled beaverboard and about half the entries referred to Grant
Wood's "American Gothic", which was evidently painted on you-know-what, which
makes me think that anybody who wants to see it in person better do so soon,
before it disintegrates into something you'd find at the bottom of a box of
shredded wheat.  This fine product appears to have been commonly used  in lieu of
canvas by cost-conscious artistes, in addition to its  application as a wall
covering.

One of the wall covering uses was in lieu of ceramic tile for bathroom  and
kitchen wainscots. It was manufactured with "tiles" embossed into the  face of
the beaverboard and field painted to look just like real tile --at a  fraction
of the cost.  The samples I got today show no such embossing,  and as noted
previously, bear no identifying marks.

Dagnabbit.

Ralph