Wait, fluorine’s a gas, right? Yes, and an impossible one to capture under ordinary conditions. This gas is likely the most immediately lethal of any natural element on the Periodic Table. You would sooner do laps in a swimming pool filled with mercury or sunbathe in plutonium’s glow than take a single whiff of fluorine. It is, in fact, so chemically reactive that it can happily eat through glass which is among the most inert of solid materials.

And that poses a problem for collectors looking to fill the ninth slot on their display case. What to put in there? Teflon, the miracle invention that lets you scrape off last week’s Mac’n’Cheese from the pan with with a flick of the wrist, is a compound that is 75% fluorine and 25% carbon. The two atoms lock into long chains so tenaciously that it becomes both a physical and chemical barrier. Those leftovers have nothing to cling onto so slide right off.

While this is clearly the poor man’s alternative, 75% is actually remarkably rich for a compound. It is purer, comparatively, than sodium in salt (at only 40%) or even the amount of iron in rust (66%). Fluorite, the typical stand-in for this element in collections, is actually less than 50% fluorine. This makes Teflon a very credible substitute; at least until such day that we can fashion exotic cube-shaped quartz traps to hold the pure gas. Best of all, it’s pretty cheap!

An unforeseen hurdle in the manufacture of these cubes was the challenge of engraving them. Usually a simple process, charring via laser produces a nice contrast to make the cubes legible. The problem, of course, is that nothing sticks to this stuff! The lettering would slide off at the merest touch. The lab overcame this problem with some secret sauce but, as you can see from the photos, success in this endeavor has only been partial… arguably a charming conversation topic in its own right :-)