11 Feb
2009
11 Feb
'09
1:26 p.m.
----- Original Message -----
From: "Brian Lanning" <brianlanning at gmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Wednesday, February 11, 2009 3:38 PM
Subject: Re: reversing case yellowing
There was a lot of talk about this on the amiga
forums. Apparently it
works great. The main problem seems to be getting a
concentrated-enough batch of hydrogen peroxide, though it's not a big
deal. The other thing is that the ultra-violet light is a key
ingredient. From what I understand, the ultra-violet light
destabilizes the oxygen bond so the peroxide can pick it up.
brian
Peroxide is just H2O2 (water being H2O). You have an unstable molecule with
an extra Oxygen compared to water (which is stable). Any heat, major
vibration, or even UV light will decompose peroxide into Water and Free
Oxygen, the Oxygen combines with whatever discolors the plastic and then
goes into solution. Heat isn't used because people are worried about plastic
warping I guess (or because the reaction is too fast). If you look on the
English Amiga Board (EAB) they have a more detailed recipe including some
other chemicals added to speed things up. Contact with metal also decomposes
hydrogen peroxide (as the Russians found out with leaky torpedoes on the
Kursk submarine a while back), but adding free oxygen to mild steel will
just rust the hell out of it in a hurry (so if you have plastic+ mild steel
parts you will have issues).
The problems I have seen with this method is some pieces do not whiten the
same and you have blotches, also some mold marks (swirling caused when the
hot plastic is injected into the mold) show up where they were not noticable
before.
I generaly just wash/scrub yellowed parts with dishwashing detergent with
"oxy" on the label, the scrubbing releases some oxygen from the soap and you
slightly whiten whatever you are cleaning (and remove dirt as well). It will
not make anything yellowed look new, but I just want the stuff clean and a
shade whiter.
Anything that had yellowed is mostly from a bad mix of UV stabilizer in the
plastic (to keep the plastic from turning into dust after years of exposure
to sunlight), and the odds it will yellow again down the road are probably
good (you just cleaned up the surface and not deep into the plastic). So you
will need a coating of UV protectand to keep anything you cleaned looking
good.
P.S. If you use concentrated peroxide much above the 3% solution you use on
cuts make sure you have a face shield, chemical gloves, and some kind of
chemical apron unless you want to go blind, ruin your clothes, and mess up
your skin for a while.