Not sure i fully understand what you said with "greenock-made spacebar" and ABS, but i assume its material / plastic related, being the spacebar might be prone to bend if too much heat is involved?
Sugestions of how to aproach the dying processs to the space bar?
Thx in advance
PBT is the plastic that IBM keycaps are made from, and can be dyed quite well.
Apparently it is more difficult to make larger items, such as spacebars, from PBT, so most manufacturers use ABS for spacebars and cases. US-made Model Ms have PBT spacebars, but the 2 Greenocks I have had, both late-1990s, had ABS spacebars. You can test with a dab of acetone (fingernail polish remover, if you have a female around) to see if it melts the surface.
The minimum temperature required to make most water-based dyes "take" is about 185 F or 85 C, and this is just about where ABS starts to soften and deform.
A full boil is much better, and PBT will handle this without a problem.