Jon? I missed who started this thread and what exactly they are
trying to do but would sandblasting be a possibility?
You can get anything from a light frost to a deep cut design with
sandblasting and it is a lot less toxic than HF.
Almost any soft, rubbery surface will repel the sand long enough to
get your design done. Sign vinyl, contact paper, masking tape,
electrical tape, silicone, Goop, your thumb, etc.
You can also make a photo resist on your own with products by
Rayzist or PhotoBrasive or send them your artwork and have them make
it for you.
An added benefit, or sometimes a problem, is that once you start
sandblasting you'll never look at any cup, glass, tile, bottle or
stone in the same way again.