Vintagecomputing is running an excellent detective story that tries to answer why consoles turn yellow and what you can do about it.

I ran into this recently; I'm restoring a PCjr for a friend of mine, and the only spare keyboard I had was yellow and dirty. I took it apart and put all the plastic pieces in the dishwasher (seriously) and, while it looks very clean, it is also still quite yellow. Read the article for some things you can try to fix old plastic, but beware: Most will actively dissolve the plastic!

Thanks for that! I hate that yellowing effect on old plastic, and it was nice to read some research on it.

I've dug my microphone from the depths of my desk, and found out the base was completely yellow. Strangely enough, I still remember the day I've bought it.

Heh. I didn't do the dishwasher thing, but I did take my keyboard completely apart and washed every piece by hand with soap and water and then reassembled it. It works *much* better and looks much better. I also managed to get rid of some of the yellowing, though most of it still remains.

My only problem after reassembling my keyboard is that I can't seem to figure out my spacebar. No matter how I set the spring, it doesn't stick up as far as it should so you can barely touch it and it makes a space.

Strangely, none of my old consoles have yet to yellow. I guess I was lucky.

You must have them in good storage (ie. no light)

Interesting...

As an ex-smoker I've always put the blame on cigarette smoke and couldn't figure out why it wouldn't clean up with spray stuff.

And I do remember somebody from an old job who thought it would be nice to spray down all the keyboards and clean them up. Oops!

smoking will cause yellowing, but of a different type. Yellowing from smoke is only on the surface, and if early enough can be cleaned off. I used to smoke, on the patch now.

Having been a comic collector for many years I'll offer this;

comic books do the same thing with age, they yellow. The acid that they come into contact with causes this. If you use acid free bags and backing for them, this stops the yellowing. With consoles this may or may not be the same problem, but I have to say that acid free environments (regardless of perspective) are important for preserving collectibles.

Or perhaps: http://science.howstuffworks.com/question463.htm

Or perhaps;

Other ways paper can deteriorate, other than light-induced oxidation of lignin, is by oxidation of cellulose and acid hydrolysis. Oxidation of cellulose occurs when oxygen molecules in the air attack the cellulose fibers in the paper causing the paper to darken and increase in acidity. Acid hydrolysis is a reaction involving heat and acids.

I love when people say chemicals or molecules "attack" something, makes it much more epic.

The article was very thorough and I actually enjoyed learning why some SNESs discolour. However, while the author mentions that heat is a contributing factor in the degradation of the plastic, he also repeatedly states that the discolouration is uniform. I would have expected the area around the heatsink on the inside of the cover to be discoloured slightly more. This however, is prying apart an otherwise excellent read.

I only wish someone who worked on the SNES manufacturing process would give some details as to the exact chemicals causing the problem? Why? Because I enjoy useless trivia like that :)

Well, it's a well known fact that the yellowing of comic books has long been attributed to acid hydrolysis which is the primary cause. This is the whole point behind acid free storage materials. Whether or not this applies to the SNES or similar plastics, I can't say, because I honestly don't know.

But aside from that, it makes sense to have a low acid, or acid free environment for ANY collectible item. I have never seen a yellow SNES, but just about every Amiga or 286 dinosaur I've laid eyes upon is yellow.