I have this deer skull that has stains on it that won't come out. I simmered it to clean it. I degreased it for over a month in dawn at 110-115 degrees. I have used the cream peroxide and basic white and it whitened up but still has these stains. I even soaked it in straight 40 volume clear and still these stains are there. Are they grease or what. I would appreciate any info.