While working at the Bell Museum years ago I was informed by John
Jaros, then the preparator at that institution, that one of the most
effective ways of cleaning mounted specimens that had become dusty
was with bread.  A loaf of sliced bread is cheap, already in usable sized
pieces, will not blow arsenic dust or other harmful materials used in old
mounts all over, and is easily obtained.

Bread has just the right amount of moisture in it to be effective at picking
up the dust on fur and feathers yet not enough so that the moisture from
the bread causes a problem.   Simply buy yourself a loaf of Wonder
Bread and proceed to wipe (gently) the dust and grime off of your
mounts.  This is probably the best way to clean mounts and perhaps the
best use ever found for Wonder Bread as well.