Working with old keyboard keycaps is less about restoration and more about damage control
I've spent roughly a decade pulling apart mechanical keyboards from the late 80s through the early 2000s, and the one thing nobody tells beginners is that you should almost never soak vintage keycaps. I learned this the hard way with a set of Cherry MX-era Alps keycaps that were caked in decades of skin oils. I put them in warm soapy water for about twenty minutes, thinking I was being thorough. When I pulled them out and started drying, the legend on about forty percent of the keys was coming off with my thumb. The ink on those particular models was applied as a surface print, not double-shot or pad-printed, and water was essentially stripping it away. The safer approach is dry cleaning first, always. Use a soft brush — a clean makeup brush or anti-static brush works fine — to dislodge the gunk. Then take a lint-free cloth dampened with isopropyl alcohol, something around 70% is fine, and wipe each key individually. Let them air dry on a towel. This method takes longer but it preserves the legends intact. If you need deeper cleaning, make a paste of baking soda and water, gently rub it on the key surface without touching the printed area, and wipe it off immediately. Don't let it sit.
Keycaps Tips Vintage: plastics, profiles, and what actually survives
You need to know what plastic you're working with before you do anything, because the treatment changes everything. ABS is the most common vintage material — it yellows over time from UV exposure and handling, and it gets brittle. PBT is rarer on vintage boards but far more stable; it resists yellowing and Shine is slower to develop. Some rare caps from companies like SA Design or early Ducky used POM, which is essentially maintenance-free but nearly impossible to find replacements for. Profile matters more than people realize. Cherry profile keycaps from the 90s have a different stem geometry than modern OEM or MX-style clones. If you're swapping in new stems or trying to mix vintage caps with a modern board, measure the stem width. A lot of Japanese vintage keyboards — think Alps and topre boards from the early 90s — use non-standard stems that are slightly narrower than Cherry MX cross stems. Forcing them will crack the underside of the cap. I once had to source genuine Topre replacement keycaps from a Japanese auction site because the aftermarket clones had stems that were 0.3 millimeters too wide. That margin sounds tiny until you're prying a cracked cap off a board you wanted to keep original. Here's something most guides skip: double-shot keycaps from the 80s and early 90s often have a secondary molding layer that separates from the primary plastic over time. You'll notice it as a faint line running through the legend or a slight gap between the character and the cap body. Once that separation starts, moisture gets in and accelerates the delamination. You can sometimes stabilize it with a thin application of clear nail polish on the edges of the legend, but it's a stopgap. These caps are past their useful lifespan if that separation is visible across multiple keys.
For yellowed ABS caps, there's no real home remedy that matches Rub 'n Buff or similar products. The UV reversal sprays you see online work on some pieces but not consistently. The chemical process that causes yellowing — oxidation of the bromine-based flame retardants in the ABS — isn't easily reversed with household items. If a set of caps is badly yellowed and you care about aesthetics, your best bet is finding a seller on eBay or Yahoo Auctions Japan who has preserved a like-new set from the same era. It's expensive but it beats replacing an entire keyboard. When it comes to stem reinforcement, I recommend using a tiny amount of super glue on the inside of the stem before mounting it to a key if the plastic feels brittle. Just a single drop, work it into the cracks you can see from the inside, and let it cure. This adds structural integrity without changing the external fit. I do this on any keycap that shows even hairline fractures, and it's saved me from losing legends during normal use. The downside is that once you've done it, you can't really reverse the process. Those caps are now permanently modified, so only do it on keys you plan to keep on a board long-term. If you're looking for references on what profiles and makers to hunt for, the Mechanical Keyboard Wiki has decent entries on legacy keycap sets and their specifications. It's not perfect but it's the closest thing to a centralized reference for vintage profiles like SA, MDA, and various Japanese manufacturer shapes.
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