This is one of the most frequently asked questions in the FMS Fluorescent Mineral Group. Folks are very creative and we’ve seen some great displays filled with glowing rocks and lit by powerful UV lights. But, as we know, UV can be dangerous to your eyes; viewers must be protected from the harmful UV rays. And a front cover helps keep that pesky dust and lint that is so brightly fluorescent off the rocks. But what’s the best material to use?
OP3! Found on many online shops here in the USA - links below. Europe another story - https://www.plexiglas-shop.com/ is one place, there may be others.
The first thought is glass. That might work but is really not the best solution. Glass blocks shortwave UV (the most harmful) and a lot of midwave UV. But it readily passes longwave UV. That can be distracting for your viewers. Sneakers, socks, fingernails, white T-shirts, etc. will all fluoresce brightly under longwave and compete with your fluorescent rock display. Worse, usually at least one side of a piece of glass is very fluorescent under shortwave. Most glass is “float glass” made by floating molten glass on liquid tin or lead. The side that contacts the tin will fluoresce a very hazy white and is unusable for a display window. But turn it around and most of the haze will go away – not all, but most (SW won’t pass through glass and cause the other side to fluoresce). But it’s still a little fluorescent and quite distracting.
Another possibility is clear vinyl – the kind used in marine applications (sometimes called Isinglass). It blocks almost all of the UV and is nice and clear although somewhat rippled. A big advantage to using vinyl is that it’s easy to lift out of the way and grab a rock for up close inspection. Marine vinyl will eventually cloud-up from the damaging UVC (just look at any boat that’s been sitting in the marina for a couple of years). But it has its applications.
Plexiglass/Lexan – there are types which block most UV, don’t fluoresce badly, and last a long time. I’ve used Lexan from Home Depot with success. But if you’re going this route there is a much better, 100% solution: OP3.
“Acrylite OP-3 is designed to meet the special needs of picture framers, museums, and artists. OP-3 protects artwork and documents from harmful ultraviolet light, which is the major cause of fading and degradation. Since OP-3 is acrylic, it is clearer and more impact resistant than glass, and fabricates with the ease of acrylic.” OP-3 is the standard for fluorescent mineral displays. It blocks UV from 400nm down, and is not fluorescent at all – zero haze. It’s easy to work with, can be ordered in custom sizes, and lasts forever. Several online distributors carry OP-3 and will even cut it to any size for you (or you can cut it yourself with a table saw):
I only use OP-3 for my displays. Every major museum that I am aware of also uses OP-3, as well as most hobbyists at shows and exhibits. It’s the only way to go….
(Additional notes from our FB Group):
Doug Bank For what it is worth, when I built my two portable cases, I needed the glass sort of quickly because the whole production was a last minute decision. I bought the panels from my local high end framing service - the only ones I could find who claimed to carry OP3. That said, they were not actually familiar with the name in the store and didn't really understand the request. They are more used to cheaper glass that has been treated to block some UV or maybe even more expensive anti reflective museum glass. Still, they took the order...
When I got the pieces, they were not OP3. In fact thy were OP2. I took a while to figure out the difference, and decided that they did the job. A 405 nm laser does pass through, but a 390 nm light does not. The difference is how OP2 and OP3 are manufactured. I think one is more suitable to large flat pieces while the other might ripple in large sections, but that one is suitable for assembly into odd shapes or entire boxes to cover something like a statue or vase.
Anyway, the point is that for our purposes, OP2 also seems to work fine.
I build a mini LW display box using OP3 for the front panel and acrylic for the sides. Acrylic is easy to work with, has a professional look, and no UV leaks out.