Gold and Silver potential stamps from Murgoth?

The ones that dropped for a short-time everywhere did destroy your item if it failed, but I would say that since these don't say it at all, then they probably don't destroy your items.

If they do, it would have caused another out-roar in the forums like what happened with Potential Scrolls a while back.

Just to ease your concerns a bit, I've used a few and they haven't destroyed any of my items upon failure. (Sorry that I don't have any screenshots to prove it, I never thought to take any.)

I've failed a few of these stamps as well, and can confirm that none of my items have been destroyed.