On several occasions I've wanted lettering/numbering printed as part of a design, but with the ability to make it stand out more effectively in the printed object without having to do detailed manual finishing. Is there a good material which can catch in and fill sunken (depth 0.4 mm, width 0.6-1.0 mm) lines/strokes of alphanumeric characters without sticking to the surface (including fine layer ridges) of the print? My best result so far has been with crayon wax, but I wonder if there are more suitable materials. (Polymer clay, perhaps?)
Results with crayons:
Durability is nice (and essential for some applications), but for many uses I have in mind it's not such a big deal. For example another place I've wanted clear text is on test panels to check nut/bolt thread sizes, in which case the text is unlikely to receive harsh treatment but any heat-based curing processes might effect the dimensional accuracy negatively. So both durable and non-durable solutions are interesting to me.