Madame Curie famously kept a jar by her bedside full of radium as a souvenir or desktop toy (hey, we get it!) unaware that it was bathing her with lethal doses of radiation. Although it’s debatable that that nightlight was the direct cause of her death (radium decays in alpha radiation which could not have escaped the glass jar) it makes for a good story. And there is little question that she handled monstrous quantities of the stuff. A good portion of the radium likely aerosolized during their extraction processes and became far more dangerous when breathed in. In any case, her discoveries soon spawned a horror show of industries selling all sorts of health potions and gadgets.

The most widespread among these turned out to be luminescent paint allowing the trendy of the day to impress their friends and associates by telling the time in complete darkness. However, just a few years later the factory workers putting together these products came down with aggressive forms of cancer and the true nature of radiation was revealed. Their story came to be known as the "Radium Girls" (recently turned into a movie) and is credited for the quick phasing out of commercial products featuring radioactive sources.

A tangible memento from this era may be found in watch hands made during those days which were meant as replacement parts; each one likely a small but direct contributor to a tragically shortened life. Each of these dials was hand painted with a dab of the luminous goo containing a few nanograms of radium. The radium is not itself luminous. Rather, it acts as an activator for zinc sulfate which is the familiar chemical responsible for glow in the dark toys. While these toys quickly dim after turning out the lights the advantage radium provided is that it continuously excited the paint. Unfortunately, the chemical is itself vulnerable to constant radiation and degrades over time. For this reason these watch hands glow weakly or sometimes not at all. This is, again, due to breakdown of the zinc sulfate and not to be interpreted as the radium "wearing out". Radium does wear out, being radioactive after all, but at the glacially slow pace of 50% per 1,600 years!

It's safe as a collectible. Just don't eat it ;-)