Buy a $1 chisel at local garage/yard sale and practice on the grinder. It's not that hard a skill to learn. And with a practice chisel, if you overheat it, no big deal, go back to the grinder and grind off the overheated section and start over.
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That is good advice on the grinder.. I have some old can openers chisels made in China by Stanley .. perfect for such abuse..
I think its good practice to do it the way I am doing it .. but I wouldn't do it for fun.. lol
Using a dry grinder isn't a hard skill to master. Crowning the wheel, as Joel Moskowitz from TFWW in his article a year or two back was the the trick that made everything work for me. Certainly, one of those seeded-gel-abrasive wheels that runs really cool can't hurt, but I've been getting by fine with my stock grey wheels that came on my grinder. I think I'd prefer the cooler wheels more because the increased friability means stopping to dress the wheel less often.
There are reasons not to use a dry grinder on your tools, but difficulty in use shouldn't need to be one of them.
Practicing on something you care less about is a good idea, but even if you blue an edge, it's not the end of the world - I've done it a couple of times in the past, but I certainly can't think of a time when I "ruined" a tool. I'm not sure how you'd entirely ruin most tools. Larry Williams actually starts his sharpening DVD by bluing the edge of a favorite chisel of his, and points out that the steel is still harder than the wood, and even if you don't regrind past the bluing, the tool can still be used, it just needs more frequent honing.