Back in the day when self-luminous watch hands were all the rage, and the deleterious nature of radium was becoming better known, an alternative that was supposed to be better was marketed in the form of promethium. The only real benefit however turned out to be that the mixture was more reliable as radium's decay was so strong it ruined the phosphors within the span of a few months while that of promethium had a gentler disposition that kept those watch hands aglow for much longer. However, the real danger of the effects of radiation were no better and eventually promethium was phased out as well.

Unlike the case with radium, Pm-147 has too short a half life, 2 years, to make a sample available to collectors even if the issue of radiation were dealt with. The Pm-145 isotope is much more stable with a half life stretching to nearly 18 years but it's never been manufactured and is known only as absolutely insignificant traces left behind from the decay of other heavier elements.

So instead we give you this beautiful photo of a jar full of freshly made promethium paint which is guaranteed to have an incredibly long half life so long as you take good care of it :-)