I got this silver eagle as a promotion for signing up for the PCGS
collector club. It was brilliant when I got it. I placed the slab in a closed plastic container and added hydrogen sulfide gas. Within maybe a week of exposure the coin was mostly covered with brownish-purple tone. Unfortunately, it wasn't really an improvement!
This experiment unfortunately didn't produce a beautifully (but artificially) toned coin, but it sure proved that PCGS
slabs don't prevent toning!