I thought I would post a quick write-up here for anyone who might one day restore a synthesizer with yellowed keys.
As we all know, ABS plastics can yellow with age due to a reaction between a fire retardant (Bromine) and UV (sun) light. Especially plastics made in the 80's and early 90's. This was a common problem with computer monitors and keyboard keys (and this solution works on both).
So I own a Kurzweil K2000 which I have been slowly but surely been getting back to good health, and one of the flaws I noticed with it (especially when compared to my other keyboards) was that they keys had significantly yellowed. In my searches, I found this open-source "product" called Retr0bright. http://retr0bright.wikispaces.com/
Looks like a great and effective recipe, but seems like a lot of trouble. Well, that's when I stumbled across this video:
At first I was skeptical, but the guy seems pretty smart and even did a few demos in the video. Plus, he got points for living in the town next to me.
Apparently, the main ingredient is this:
I couldn't help myself, so I tried it.
The Creme itself is only about $5 at Sally Beauty Supply. It is mostly hydrogen peroxide, and already a gel-like consistency, which is great for staying put on yellowed plastics.
After getting good results on an old test key, I put it to work.
Here are the steps:
1). Remove the keys and wipe them down.
2). Wearing gloves, apply a liberal amount of Salon Care Creme to the surface that you want to lighten. This is best done over the sink. I used a small paint brush for application.
3). Place the keys in a dish in a way that they can be held upright. Keys are irregularly-shaped, so this can be tricky. I used a Pyrex casserole dish with some rolled up cardboard tubes to support the front and rear of the keys. I was able to do about 8 per batch using this method.
4). Place the keys under a UV light. Blacklights can work (though may take longer), or you can use natural sunlight. Personally, I used a UVB light from an old reptile habitat. The lamp was a 10.0 strength, and it worked very well.
5). Put plastic wrap over the keys to keep the Creme from drying up.
6). Be patient... I treated each set of keys under the light for 24 hours. You could go longer or shorter, depending on the amount of yellowing. I found that only a few hours made a difference.
At this point, things should look like this:
7). Take the keys back to the sink and wash them thoroughly. Repeat the treatment if necessary.
8). Reinstall the keys and enjoy! Here are my results between treated and untreated keys:
The keyboard is bright white again:
I have my doubts that this would work on ivory keys, but since the effect is the same (UV light causing discoloration), it might be worth a shot. Perhaps I'll buy an old piano key on eBay and do a re-test. Real ivory might be hard for me to find though -- not sure if there are trade lays prohibiting that or not. The process works very similarly to teeth whitening, so for all I know it could very well work. Some electronic organs used other types of plastics, so the verdict would be out on them as well.
Overall, this is a great solution to yellowed keys or vintage computer parts and I highly recommend it! I also recommend going to a pet store and springing for a UVB light. They are expensive (around $30 even for a cheap one), but the result is worth it.