If skins are to be kept some time they should, after a preliminary pickling, be put in new, fresh pickle and it should be occasionally tested with a salinometer and kept up to the original strength.    From Wordnik.com.  [Home Taxidermy for Pleasure and Profit A Guide for Those Who Wish to Prepare and Mount Animals, Birds, Fish, Reptiles, etc., for Home, Den, or Office Decoration] Reference