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Restoring the appearance of scratched plastic boxes
Most mineral collectors have stashed away somewhere a bunch of older thumbnail ("Perky") boxes and other display boxes that are all hazy, scratched, and just plain not nice to look at any more. Sometimes they get so hazed up that it's impossible to see the mineral specimen clearly through the plastic.
Clear polystyrene plastic as used in display boxes has a Moh's hardness of something like 2.5 at the most. Dust particles trapped on the surface of the skin play havoc with a shiny, clean surface of polystyrene.
When the box size is a common one that's easy to obtain new, it often makes sense to discard the scratched ones and get some new boxes. However, sometimes a box is of a discontinued size or proportion, or maybe the collector just doesn't want to wait until new boxes arrive in the mail. Herein are some helpful hints about cleaning plastic boxes, especially the acrylic and the polystyrene ones most commonly encountered in mineral collections. At the very least, the reader can get an idea of what not to do, from someone who's already ruined quite a few boxes experimenting.
What not to do:
1. Don't use paper towels or even ordinary tissue paper. These will haze the plastic.
2. Don't use sandpaper-- maybe this seems obvious, but even the superfine automotive sandpaper is too harsh. 1000 and even 2000 grit are completely useless except as early-stage grits in a succession of ever-finer papers. You would need perhaps 5000 grit or finer.
3. Don't use a motorized polishing tool! The heat buildup is extremely rapid. It can melt and smear the plastic before you even know it. By this time, forget it. The box will be ruined for good.
4. In most cases, don't use acetone. It will dissolve and re-float the plastic surface, but it won't dry smoothly enough. It usually dries with a frosted look that's worse than when you started.
5. Don't bother with cerium oxide or other lapidary polishes on plastic. The particles, which work nicely on stone, seem to do more scratching than polishing when it comes to plastic. They also work themselves into the plastic surface and don't come out easily.
6. Don't press too hard! Time, not heavy pressure, is the key.
What works (and what might work):
1. Use lint-free cloth, preferably with all-cotton fibers. Avoid paper, generally... unless it's micro-weave, such as for lenses.
2. Specialized lens cloth or "delicate task" wipes, such as Kimwipes EX-L with LintGuard, are decent for polishing clear plastic. If they're good enough for precision equipment, they should be good enough for a 99 cent plastic box (even though the plastic is even softer than most lenses!!). These wipes seem to do the trick, sometimes. A hand rubbing with these alone can restore an acceptable polish to hazy or very mildly scratched plastic boxes.
3. Some of the commercial plastic polishes are good for restoring plastic boxes, but a lot of one's success depends on the cloth used (see 1 and 2, above). The polish should be one designed for clear plastic.
4. After a prolonged but mild rub-down with microfiber (with or without plastic polish), experiment with various automotive waxes. This will also require cotton or superfine paper cloth. Waxing is sort of cheating, but not as much as oiling (see 5, below).
5. If all else fails or you just don't want to try the other methods, you can oil a soft cotton cloth and wipe the surface of the boxes. It takes only a tiny amount of oil to hide much ugliness. Use something relatively odorless, such as 3-In-One. Oiling is a cheap sort of trick, but it works in a pinch when you want to show off your minerals to some people at a show and don't have time to wait until new boxes arrive.
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