I decided not to touch this, but if one wanted, I believe a light swipe with a damp paint brush across the surfaces of the individual watercolor blocks would remove whatever light scattered soil sits on their surfaces (I don't think they've been touched in well over a hundred years) and make them all look bright and (old-)new again. This is a "toy" watercolor set, meaning the blocks are smaller than full scale in size, I believe dating the 1850s-60s, manufactured by Lewis Haehnlen, Philadelphia, featuring Osborne paints. (George Osborne was among the first American companies to produce watercolors equal in quality to European colors.) Clearly some of the blocks were relocated at some point, not necessarily matching the names of colors printed along the bottom of each slot.And then 10 extra blocks here as well, set in the niche where a small paint brush or two would originally have been set. There could absolutely be put to use now, and with a wide spectrum of colors here to use--but of course early sets like these have also become highly collectible things, and to my sensibilities are quite beautiful and romantic feeling things. 

Box 6 7/8" x 4" x 1". All pictured included. Some colors never used, some lightly used. Papered label on lid of box worn with notable rippling and a few cracks/tears. Hook on front does clasp but does not hold super tight. Box itself in good structural shape, hinges well attached.