hi,
sorry to miss your question,
paul_c5x4 pretty much said it ...
you need to coat each side of the glass separately.
when i was doing collage work like this, i coated one side with minwax polyurethane
and let it dry. i coated it with a thin coat of liquid light with a sponge brush
( you can use anything to coat with, pour it &c. i had an old conair hair drier that i put on "low heat"
it still got hot just it didn't glow red and maybe fog the emulsion.
when it was dry ( not tacky but hard and smooth to the touch ) i made my exposures. don't forget a negative will make
a positive on the glass and a contact print of the glass will be a negative again. you can also make paper positives ( regular prints )
and contact print THEM as a negative on the glass, so the final will be a positive ..( seeing you have the liquid emulsion if you want, you can
coat thin paper so it is easier to contact print ) ... once you get one side full of images you wash off the 2nd side of the glass
and repeat the process ... the glass will have images on both sides which you can then transfer onto photo paper ...
with the liquid emulsion on the glass you can coat and reexpose as many times as you want ... if you are using 7x5 sheets of film
you can expose things in darkness ( maybe reflective meter read? ) so you can doubl expose on the film or sandwich negatives &c ...
darkness = clear so it makes things easy that way ..
good luck !
john