I've stained trichodinids & sessile ciliophorans for many years using Mayer's & Harris's haematoxylin successfully. Lately a few batches of stains destained few months after initial stain. Has anyone else picked up this problem? I have been wondering whether it's not the mounting medium, we use Eukitt & Canada Balsam. Lately these mediums are very watery when bought, I was wondering if xylene-content is not affecting stains after a period?