Pipyr, it has been quite a few years since I have used LL, but from what I recall, the regular stuff was rather weak and needed at least two coats, and that was on paper. They used to make something called AG+ that was rather nice on an absorbent paper, but that was a long time ago and I don't know if they still make it. I would have to assume that with glass, and it's lack of absorbancy, that you would need at least two coats of LL if it is the regular stuff. If you are intent on doing a lot of work in this area you may want to look at an emulsion that is more silver rich. I was on Photographer's Formulary the other day and seem to recall that they had an emulsion. I think Foma also has an emulsion. I could be wrong about these, though I wish you luck.