I think treated lower one appears sharper. Does this theory sound reasonable at all?
I dyesub fabrics in my business (for the past 20 years), and we experience this sort of bleeding once in a while. What we do is we reverse print to paper with dyesub inks, which are then sandwiched on top of our target fabric. Then we run them both through a heatpress. The press gets to a high temperature and the pressure holds everything in place, so there's no slippage.
The way it works is that the ink (started as a liquid) is now in a solid state on the paper, but under high heat will become a gas -- skipping over the liquid phase entirely -- and work its way into the fibers. But still, even as it is a gas, there's
some expansion of the gas, which is what probably accounts for the fuzziness. Once in a while I have a client who wants a super, super thin white rule line, on a black background -- and if it's thin enough, it will "fill in" a bit. If my pressure settings aren't right, it will be worse. Also, after coming out of the press, the paper and the fabric have to be separated and stay separated, or a double-hit shadow can occur. Also, putting down more ink than is actually needed will "blow-through" to the backside of the fabric. So I use a third substrate, a tissue, to catch that outgassing.
So, based on that, I think that's the phenomena you're seeing with the keycaps -- outgassing. The ink becomes a gas and doesn't go perfectly down into the substrate, it feathers out a bit. That said, I have no real idea how the keycap manufacturers are dyesubbing their caps. Maybe they're using the vacuum-sealed film (seems like overkill to me, but ideal if you were going to dyesub the
entire surface of the keycap), or maybe they've just got a jig that allows for paper and a sandwich press sort of heatpress. I could see the paper route working if they're doing whole trays of just a single kind of letter, and they blanks are cheap enough.
I would love to see someone use the film to dyesub the entire surface of a keycap -- just so you could say it's been done.
Right, sorry -- damorgue, your theory is absolutely plausible. The contrast between the black-on-white is what makes the the black-on-gray look so much better.