Hi all! Went to Taxidermy school but had to learn euros from YouTube... Mounted one on a beautiful habitat and it was nearly ready...until now! It was an old skull - it was already rotting when I got it. I cleaned it and degreased on simmer in oxi, then in a tub of warm water used an air gun to get everything out. Then I whitened it with 40V and basic white. It's mounted and yellow splotches are showing up everywhere! The other skull I did using the same method has a few tiny yellow marks as well. What can I do to fix this? Your input is VERY appreciated!!