Found this while going through the boxes of my old coin collection. Took it to my friend's pawn shop to get it tested with his handheld gun, as well as calipers and a scale. It checks out. Found an old receipt with it from 2009, which I apparently paid $970 for it. Got a new capsule for it because I had it in a nasty plastic flip. Apparently I didn't know how to take care of this stuff back then because it's full of fingerprints and a few scratches. No wonder I misplaced it I forgot I even had it. Anyway, here's my nasty grimy coin. Adding it to the rest of the pile, where this time around it hopefully won't be misplaced or mishandled anymore
Your nasty plastic flip was probably made from PVC plastic and that's probably some PVC residue on that coin. Now, PVC won't harm gold, but I still wouldn't want it in my collection. This one I would not describe as crusty - a term we use for toned coins with patina and skin. "Crusty" is a positive term. I'd say this one has a residue and requires conservation. That's a bit more of a negative implication. Luckily, the answer is a quick bath in some pure acetone. Perfectly common, safe for your coin, and won't harm you as long as you take a couple of basic precautions. But, it will remove the residue and improve the appearance of your coin.
Thanks for the tip. I do have pure acetone around. Used to keep that stuff for my silver coins when I collected ancient coins as part of my cleaning process. I'll take your advise and give this one a good acetone soak.
Going to wait to dip it in acetone to remove fingerprints and other unwanted stuff until I've ordered more quadrum capsules of the correct size to house it in. I'll leave it in this tight fit capsule in the meantime. However, here's a nicer shot next to my Britannia so you can really see the contrast between a 24k coin and the Krugerrands.