I've contacted a lot of prints on Brovira, which also has logos all
across the back ("Agfa"), but for some reason they DON'T print.
Actually, this is very old Brovira (about 25 years -- old #6, new #5),
amazingly it's still excellent.
As for getting good contact, answers from the list more or less parallel
my experience, except I'll add that an RC paper lies flatter, so if you
can BRING yourself to print on RC, you should have less trouble contacting.
My prints were all on doubleweight fibre base, however, and I didn't get
good contact larger than 8x10 until I bit the bullet and bought a vacuum
easel. It's a monster, bent on waking the dead & making SPARKS that
terrify me each time I turn it on, but contact is good.
Short of vacuum easel, heavy glass-on-glass is probably required for larger
than 8x10. We use plate glass on thin-foam covered board at school (less
breakage than glass-on-glass) and clamping all round is a BIG help.
Another help is a glycerine bath after final wash for your fibre based
print (if someone asks I'll look up the proportion, maybe 1 to 20).
Another help is flatten the print in drymount press right before exposing.
Cheers, Judy, NYC
PS. I don't mean nice little bulldog clamps either, but heavy carpenter's
clamps or c-clamps (pad the glass).