Thanks all for the wealth of information and the warm welcome to the forum! You all have provided me with great starting points for my research.
I'm not interested in creating custom cases and crystals, but using commodity parts. I may be more height restricted going this route than I would be with a bespoke case & crystal, but there are some nice commodity high-domed crystals that might give me more room to work. The note about hand extenders is a great one, however, as it'll probably be easier to get to a 1.0mm height with a dial than an 0.4mm height.
I agree that hour markers, etc. will be infeasible due to the precision required. A better solution would be adding a
chapter ring, as Tag Heuer did with this fordite watch:
I've done more research since my original post, and I absolutely agree with @R.U. Sirius's suggestion to look into opal doublets and triplets -- a very thin opal doublet is probably a very good model of how to accomplish this.
To this point, does anyone know how thinly opals are sliced for doublets and triplets? I'm guessing that the answer is *really* thin, and the tools and techniques necessary to accomplish that are probably the right track for me to pursue for my project. I know that opal doublets and triplets aren't exactly embraced as good things, but I'm quite curious about the techniques necessary to create them. I'll be Googling this, but wouldn't object if anyone knew this information offhand. ;-)
Shoot, with a thin enough slice, it'd be trivial to mount my "stone" to a blank brass dial and take advantage of the brass dial's feet, etc.
As far as tools, I'm going to be looking into slabbing saws and lapping machines to start. As a total newbie, I know very, very little about these. My instinct is that it'd be easiest to get a nice thin slice with a larger diameter (12"?) thin-bladed slabbing saw. There's a local lapidary club I might look into to see about learning how to use this equipment. My instinct might be totally off, though, is this the sort of application that a smaller diameter slabbing saw might be better at? I feel like the cutting ability of the saw will be less important than how precisely it can be used -- forgive my lack of terminology, but having a precise way to smoothly and evenly feed the material to the saw sounds more important than the saw's raw power. Getting a "thin enough" slice to feed to a lapping machine to work down to the final height seems like a better option than trying to hit the 0.4mm slice target using only a slabbing saw.
And for the actual dial materials -- I'm honestly more interested in experimenting with weird but inexpensive stuff than expensive and difficult materials like opal. The idea of a fordite, "surfite", or "bowlerite" dial is what is really driving me here -- I'm absolutely in love with the fordite dials on those Tag Heuer watches. Not only are these synthetic materials inexpensive and cool, but they appear to be fairly easy to work with. See, e.g.,
this desktop CNC mill shaping fordite. Fordite has specifically been compared to rhodochrosite -- 3.5-4 hardness, but brittle. The techniques required, however, seem squarely in the realm of the lapidary. And I certainly wouldn't say no to an opal or lapis dialed watch, if I figured out the technique!
Anyway, thank you all for the warm welcome and great information! I've got a lot more research to do. I'll keep updating this thread as a I figure stuff out, both to track my progress and to help other folks out if they're researching a similar idea. I'm a huge believer in open source information.
Cheers,
Dan