I want to print two photographs, then glue them back to back, and laminate the result. what glue should I use? Is 3M Spray Mount spray suitable?
I have done some tests. I made some business card sized images and printed them on Xerox paper, matt coated one side, 95 gm/square metre. To form a two sided image I printed, using an ink-jet printer. The front and back were adjacent so that I could fold the result. I used Staples (the office supplier) glossy 125 micron (each side, 250 micron total) thick pouches and a domestic laminator.
No glue and left a margin of transparent laminate around the paper. This was ok, but I didn't want the margin if I could avoid it.
No glue and cut off the laminate at the edge of the paper. I thought it possible that the laminate glue might penetrate the paper and glue it together. No such luck, it remained as a folded sheet.
I glued the folded paper together with 3M Photo Mount spray and laminated the result. However vapour from the glue made the laminated result bubble up, although it shrank back to a flat card after a while. Trimming the margins off left me with a viable result with the images going to the edges of the card.
Did the same as (3) but I left the glued paper in a warm place (an airing cupboard) overnight. There was no bubbling and the final result was what I wanted.
I frequently use 3M Spray mount or similar for mounting photos. There is also a photo specific version that is slightly more friendly to the dies and such in theory.
If you are laminating the result, really even something that is minimally tacky should work and might give a smoother result since it would be a thinner coat and only needs to hold it in place until the lamination.
Most recommendations concerning what glues and cements are best for photographs, stem from the days of chemical-based prints. We are talking silver/gelatin black & white and dye/gelatin color prints on conventional chemical-based photo paper. These recommendations steered you away from cements with low pH and chemical content that could damage. All sound advice. Chemical-based silver/gelatin prints are attacked by sulfur, and chemical-based color prints are comprised of organic dyes that persist only if the pH is within a narrow range.
Further, both the color and the black & white images were bonded to the paper using glue made from gelatin. This is the same gelatin used to make tempting desserts. Pastes and glues that absorb moisture are no-nos; the moisture migrates to the gelatin. Add water to gelatin on paper (or film) you get a tasty meal for mold and other beasties. I think modern prints produced by inkjet and the like are more robust. Not to the point that we should throw caution the wind, but not to the point we should become paranoid as to what glue or pastes we should use.