tintin wrote:
Just out of interest (as my amiga 4000 is being sold as we speak), is there any explanation why some parts of the front cover might yellow more than others, isn't it all supposed to be the same plastic ?
On my (ex) amiga the front cover is still sparkly white (well, as white as it ever was, more like a light creamy colour) only the cover plate of the floppy is more yellowish, same is true for the keyboard. All parts of the amiga have always been in the same spot.
Contact with compounds that can oxidize the plastic and/or oxidize themselves (skin oils, etc)... Airflow from the fan pulling crap in through the floppy drive... Differences in heat at various portions of the unit...
Dunno about the Amiga plastic, but yellowing in general can be caused by all sorts of things. On this era of stuff, I imagine we can also count outgassing of PCB/component resins (and solder rosin/flux) as part of the problem; that, with the electrostatic effects, probably accounts for the 'monitor-shaped-footprint.'
Smoking is another great culprit, of course - somewhat oily particulate in the air, loves to condense on plastic. I had a monitor I thought was just nasty and old, until I realized I'd been parking my ashtray half-beneath it; a bit of regular Windex, and I realized I was just getting a view of what I've been doing to my lungs.
My favorite technique involves good ol' Borax, though I haven't tried it on an Amiga. Obviously, you want to do this on only the plastic - don't try it while there're components inside. Take a small amount (tablespoon or two?) of borax, and a sponge soaked in hot water. Dump the borax on the dripping sponge, so enough of it dissolves, but some remains as a particulate for scrubbing (probably still gentler than sandpaper!). Give the plastic a good going-over, being careful not to pick up anything in the sponge that'll gouge it (use judgement), and if you're lucky, the dinge will just disappear before your eyes. (Particulates will scrape off, and otherwise, the borax has a bleaching action that, hopefully, shouldn't yellow or degrade the plastic too much.)
Rinse the whole thing with plenty of hot water when you're done.
After that.. I'm not sure what you can use to protect it. A long time back, someone discovered the same PABA used in sunblock could be added to deck stain and the like, and that's where cheap UV-protective wood finishes came from. But sunblock is going to be, well, gooey, and plastic-protectants may or may not be what you want. (*Maybe* something like Armor All works; I've noticed it seems to dry out automotive vinyl *faster* once it wears off. Other things contain urethanes and other weird stuff that might turn out to yellow on their own anyway, no matter how 'UV-protecting' they claim.)
I've tried a little UV-protective furniture polish (in other words, light mineral oil, hint of lemon, PABA) on the fax machine here; can't tell if it's an improvement or not. The sunblock should help, but the oil seems likely to yellow anyway. I think the best you can hope for is 'trying whatever you think will work' as a protectant, and using the borax technique again if/when that fails.
Assuming the borax technique works on whatever's happened here, anyway. Someone mind trying it on the Amiga plastic and providing some evidence one way or the other?
(Oh, and I wouldn't use it on the Transformer - or, at best, I'd go with a Q-Tip on the white portions - because I'd fear it'd degrade the red/painted bits.)
