While replacing the casters on circa 1918 Apollo player piano
I found what looks to be a cardboard spacer under the rear caster
plates.  The cardboard is very dense, dark in color, and looks and
feels almost like leather.

Is there a type of cardboard commonly used for shimming casters?
Was there some type of treatment applied to it originally?

Jim Slyger

 [ The shim material might be red pressboard, used in
 [ letterpress printing as backing and in electrical machinery
 [ as insulation.  See the article by Richard Vance at
 [ http://www.mmdigest.com/archives/Digests/200211/2002.11.08.05.html 
 [
 [ At http://www.gpo.gov/customers/text/vol11/107.htm is what seems
 [ to be a U. S. Government Printing Office purchasing specification
 [ for pressboard, in thicknesses of 0.015, 0.020 and 0.025 inch.
 [ -- Robbie