I recently acquired a little ultrasonic cleaner, so I've been disassembling and cleaning all my keyboards. Throwing the keycaps in the ultrasonic cleaner for 10 minutes with a couple of tablets of denture cleaner works wonders.
While I've had each keyboard apart, I've been cleaning up the case/body with isopropyl alcohol and cotton wipes. This has worked without any concern until I got to my first NeXT keyboard. I noticed as I was wiping the keyboard body that my cotton wipes were getting very black, much more than with any of my other keyboards. Growing concerned that I was actually removing the surface of the keyboard case, I stopped. No visible damage done, fortunately.
But this raises the question: Is isopropyl alcohol a no-no for cleaning a non-ADB NeXT keyboard, or is my keyboard just really, really dirty?
I have unfortunately made the same mistake.
Well, luckily I noticed pretty quickly that it wasn't looking like most of the dirty keyboards I've been cleaning up, so I stopped before doing anything that shows. Lesson learned. Soap and water only on NeXT keyboards. 8)
The keycaps of nonADB keyboards are another issue I just realised today by pulling one ore another cap loose. Everything inscripted not just on top of a key is paint! I.e. you can use Isopropylic Alcohol on keytops only as those keycaps are produced in the double shot injection mould process. This not only applies to white labeled keys but also to the green ones like the 'command' keys. Never ever use IPA on keycaps fronts like 'Alphalock','Mute','Undo','Cut','Copy','Paste'.
If do not like the idea of reading ancient passwords in the polished look of keycaps then you are also safe to use slightly abrasive cleaning methods like a power cleaning sponge. That helped freshen the looks of some utterly worn keys for me.
I find that the ultrasonic cleaner + denture cleaner tablets mentioned in the first post works great on all the keycaps I've tried, including the NeXT's. It doesn't involve any rubbing or any harsh solvents, and it's never failed to make keycaps look like new again.
Won't fix worn keys of course. :)
It depends on the history or make of the keyboard if it resists short wipes of IPA more or less. Today I have cleaned my 2nd keyboard it did well resist 99% IPA which I always use. You just have to avoid intense soaking of more than a dozen seconds. No problems then. If the surface happens to become cloudy another quick wipe is able to heal it. I always use lintfree medium grade microfiber towels. I admit I have a lot of experience in materials and chemicals from my personal history of model building and classic car paint restoration.
The NeXT keycaps are nothing special at all compared to any other contemporary manufacturer. NeXT casings are special. We can be lucky that this soft coat paint job does not suffer from the problems any 15 year old Volkswagen interior is suffering from: namely flaking off. As initially mentioned that depends on environmental conditions such as heat and sun. This might make a difference in chemical resistance between NeXT devices.
I have a NeXT mouse that has some kind of partially dissolved rubber rim. I could bet it was used by a woman who used to lotion her hand regularly in the office ... it's mainly mineral oils that attack rubber and the like.