Sandwiching between glass...
Don't do it!
I agree with ROL on this.
Trying to mount a print by squeezing it between two pieces of glass is bad practice in many ways. For one, it doesn't look good, in my opinion, but more importantly, it's bad for the long term life of the print. You don't want something touching the front of the print, that's the whole point of a window mat in traditional framing. When (not if) you are met with humidity & temperature changes, the print will expand & contract and if it's in between two pieces of glass you're going to get serious problems with waviness of the print and worst case scenario, you might get gelatin stuck to the glass surface and eventual print damage.
Now, to somewhat contradict myself, there
is a technique called face-mounting, where the image side of your print is stuck to a sheet of glass/plexi with adhesive. This is by no means considered archival, in the sense that once you do this you're never getting your print off the glazing, but this is something that you'll see done by high end studios. So it's a viable technique, and it could in theory withstand the longhaul, but if the plexi glazing is scratched or the glass glazing is broken, you're done. It's definitely "a look" though.
So take what I say as food for thought if anything. A 3M mounting adhesive specifically designed for photographs should be groovy and there's also a 3M product called PMA (positionable mounting adhesive) that would allow you to do similar things.
