I had thought it should be possible to clean them, there's not much difference between plugs except sizes. I'm glad to hear you've done it many times.

In any event, I wonder how barryB tried to clean his plugs? There is a right and wrong way to do it, maybe he'll post back how he tried and failed and we can learn from that. As to how I did it, I used the Champion spark plug machine my buddy had, but now that he's passed away I'll have to look for another source. I guess I can ask my A&P to let me use his, we get along well.

As I've been given to understand, certain types of media will wipe out a plug quickly, and others are ok. I.e. I think sand is a no no because it might have a couple particles remain which then fuse and turn into glass when you use it.

Normally on an aviation plug we use a pick if we can to remove the lead deposits. But we always pressure test them afterwards to insure they're going to work in an engine. Just because it sparks does not mean it's good, they can and often will quit under load and that's where the machine was useful because it would place them under a load during testing.