You're not wrong Martin. UV light is exactly what causes all the yellowing. So if Mikyok wants a nice yellowed RK, just set it outside for a summer. Take it to the beach. It's not smoke although I'm sure that doesn't help. It's all UV.I may be wrong, but I've heard that if you leave them out in the sun, they will yellow up.
I guess I should correct myself, the yellowing isn't under the surface, or on the surface, the yellowing is a chemical change in the acrylic itself. Peroxide and UV light actually reverses that chemical change. I find it odd that you use UV to fix UV damaged plastics.
The recipe is no longer up there on that old website, but I will explain how I did it.
As an aside, this stuff also works for the acrylic enclosure surrounding you car's headlight. You know how they get all yellowed and nasty looking? That's UV damage. Cure below:
What I do is I make a 10% peroxide solution by diluting 35% food grade peroxide (strong stuff, don't get it on your skin) with distilled water (important that it's distilled) so it's a 10% solution. Then I add thickening agents to make it into a gel so it sticks to the shell, (I think I used guar gum) and a tsp of oxyclean mixed with the gel right before application.
The oxyclean supercharges the gel with even more peroxide, and it also makes the gel expand, so use a container with no lid, like a pitcher, or it will explode. My half full pitcher overflowed, so take precautions. Paint the activated gel on the drum with a paintbrush, (DON'T SCRUB IT ON WITH A SCRUB BRUSH!) right over the hardware if you want, and set it out in direct sunlight to reverse the yellowing. It's friggin magic.
You do have to rotate the drum so the shaded side gets direct sun. I made a spray bottle of distilled water and oxyclean and I would re-wet the shell with it when the sun dried the gel up. I don't know if this is necessary, it's something that wasn't with the instructions. I just did it for good measure. 1 good sunny day and you're done. You do have to clean the dried gel off with regular water. Do all this in crappy clothes in case the peroxide gets on them, which it will. This gel behaves like bleach if you get it on your clothes or skin.
By the way, bleach supposedly unyellows wraps too, but do not use bleach on your wrap. Bleach will bore tiny pits in the acrylic. Peroxide is totally safe for your wrap. It's a cheap fix that's gives fairly astounding results.