I'm fairly new to coin magic (after being strictly cards-only for years), and so have been practicing classic palming. The issue comes from the fact that I've been using old Irish 1p coins; they're very tarnished and when I palm them, that rubs off on my hands. While this makes it look like I've got bruising from practicing so much, making magic look almost 'hard' (in the 'street' sense) and earns me points with people that can't guess the actual reason, it concerns me that this could well be a bit of a give away in performance.
Anyone know of a way to keep the coins polished, or some other way to stop this?

There is a product called semichrome that is made in germany. We can get it in the USA. It has worked on every metal that I tried it on. Copper ,silver, magnesium... you name it. Highly recommended.

I actually get the marks from polished coins, copper coins, silver coins, clad coins... (I hope you got the picture by now)

I believe it just comes with the move. I do however notice it more if I use a little violin rosin on the edges (as David Roth has suggested before). BUT...All that being said, I think it is a "running without being chased issue" that we all face from time to time. I have had light rings to dark calluses thru the years and have NEVER been called out or even questioned about it. I have had people "speculate" that I was secretly holding the coin at one point but I openly flash both palm up and palm down hands with fingers spread and ask "Where???" then hand them the coin and ask them to show me. (only for the guy that really is going out of his way to challenge me), They often stick it near the right spot only to drop it immediately and give up.

I do not think they hurt you unless you really bring attention to them.

The same problem happens when I play French Horn on a horn where the lacquer has come off. Usually washing my hands with a mildly abrasive soap gets it all off. If you get clammy hands the moisture could also contribute greatly to this, and drying your hands often should help. With a horn I can put some felt over the contact points to prevent this, but with a coin you might want to try coating it with clear nail polish. Hopefully this helps, let me know what works and what doesn't.

Cheers guys. I'll have a play with the option you've given me. It's not like I'm at performing standard yet, so it's not exactly urgent. Tbh, coin magic scares me much more that card magic. Far too much acting and pretend to pick up/drop coins...

Try to hold the coin more lightly.
Classic palm should be light enough that you can tap the back of the hand and the coin will fall out. Adjust a little more pressure if needed for routines. you do not need to hold it super tight though.
The tarnishing leaving a mark has never been a problem for me. Us the advice given so far.

Hope that helps.

I use silver coins personally and don't seem to have this problem

I was going to offer the same as Mobius303. You should use just enough pressure to keep it in place. If you are going light, might want to try a different coin that won't tarnish so quickly. But I imagine some of that could be due to the oils, and sweat of your skin.

The irony of developing callouses through excessive force is that this allows one to hold a coin in CP with nearly zero effort! This not only makes for a good looking CP, it frees up a few extra neurons, which can then be used to focus on more difficult bits.

I've also had ( ) callouses for years: after a while yours will (likely) fade to where they are basically invisible. Oh, I've been playing stringed instruments for decades: the tips of my left hand fingers feel like leather, but look 'normal'. So, fwiw, I recommend you keep up the shredding.

Sorry for the late response, missed this one I guess...

Good way to build that cp is to practice the muscle pass. It has greatly improved mine