We've had various experiments with "using laser engravers to make custom keycaps" for over a decade. But in general, this either meant one of two things: You milled into the keycap so you got a sunken texture but no real contrasting lettering, or you fused toner or ink into the surface of the keycap so you got a darker lettering.
But you could hardly do light figures on dark caps. Until now.
The other missing piece of the puzzle was the old experiments in using off-the-shelf fabric dye to recolour off-the-shelf caps.
This tends to sink into the PBT material only at a very superficial level, so if you use the laser to vapourize the the top tenths of a millimetre of plastic, you cut through the dyed surface back to the original light keycap.
Hence the term: Laser Ablated Reverse Dyesub (LARD).
This is also reminiscent of some of the early "shinethrough" keycaps (Deck/TG3) where there was a thin coloured layer that was cut through to create the transparent glyph.
I've tried it with some cheap white PBT caps (apparently a Massdrop offering for some old Preonic group-buy). I selected it because I wanted different row keys, and it was cheaper than buying a full 108 setup. Unfortunately, it has way more bottom-row caps than I need but a shortage of top-row so I'll probably have to get more caps to finish the top row.
Used the common Rit DyeMore they sell at Walmart, with some salt (not sure if necessary), then heated up in a disposable aluminium pan. The first few caps went in before it got to temperature and took like 15 minutes to darken, the rest took far less time.
I then used my little NEJE DK-8 engraver with a 1500mW head. This is one of those toy-engravers made from the mechanisms of DVD-ROM drives, so you only get limited control (raster image, and a "burn time" control instead of a power level. I tried with 80ms/dot, 90ms/dot and 100ms/dot withiut significant difference in outcomes. I'd suspect the sweet spot is "enough to burn through the dyed material that absorbs the laser well, without too much darkening of the underlying white PBT once you break through" and "not so long that it starts to blur the overall image". There may be better tricks with more sophisticated lasers.
When it comes off, there's often a dust halo, probably some portion of the dyed PBT vapourising and precipating back to surface. Use hazard precautions.
The overall look is probably "as good as the keycaps on my original Ducky 1008XM, at least" (Its lasered caps started as a weird bronze colour and aged poorly). I'm not sure how they'll fail-- the dye might rub through on other areas of the cap, or it might accumulate filth in the engraving. The characters can be felt because of the depth of engraving, it reminds me of the old Chicony rubber-dome my parents used for like 15 years where they had worn the filling out of some of the engraved legends.
Possible directions for future research:
* I'm assuming black dye is the best case scenario for this-- most likely to soak up the laser and burn through. How well do other colours fare? What about using other colours "underneath" the dye?
* Tuning the dying and lasering process for maximum contrast or preferred and repeatability.
* Followup cleaning or treatment processes to try to clean out the engravings and maximize contrast.
* Combining the engraved characters with paint or other filler to enhance contrast or change wear patterns. I've drilled fairly deep with the laser before, but I've never been able to get results I liked from filling processes. Maybe "bootstrapping" it with the bleed-through base colour will help.
