I usually send coins for conservation before grading. Several times last year I had staining developed after grading on some silver coins that were perfectly fine in OMP. That always happened when the turn around time was relatively long, 2-3 weeks or so. In other submissions where the coins were conserved and graded within short time I had problems at all. I don't know if it is just a coincidence, my bad luck, or something related to the amount of time the coins are exposed to air after conservation is complete and until they are being placed in holders. Any idea are the coins are being stored after conservation?
That unicorn has 'special' staining that highlights the frosted areas - around the unicorn, the Chinese characters, the flowers. Very strange.