cupping in dry mounting on mat board

Ok, Michael and Paula are in Europe, or I would ask them.

I just got back into darkroom work after many decades.

I mounted several 8x10 AZO prints on 4 ply archival board with seal drymount tissue using the
following:

Prints were treated with fixer removal (kodak) agent, washed for an hour, screen dryed-next day
re-wetted in a tray, squeeged and dryed in the mounting press between two sheets of mount board.

Next day, tacked to 4 ply mount board (archival) with the mounting tissue, and mounted in the press for 4 minutes
at 200 degrees. Removed from press, let press cool to 150F and put the prints back in the
press between two mount board sheets and left overnight.

today, they want to cup, in the long dimension-they are on 11x14 board.

Is the cupping normal? I do not remember this happening when I was doing the same thing
back in the 1950's, although I used double weight paper in those days.

Help is greatly appreciated.

Herb,

Ouch ! 4 minutes at 200 degrees seems way too hot. I'm at 1-1/2 minutes @ 175 degrees. Longer time and/or higher temps = permanently bent (curled) boards.

But, maybe I'm missing something. My press is very old. A Kodak type E - about 1945. Still works fine.

Your procedure sounds a bit elaborate; after drying on screens, you should be able to (gently) flatten any curled-down edges so that they don't get bent under, and slide the prints one at a time into a warm dry-mounting press. After about 15--30 seconds, take the print out and immediately hold it flat on a cool surface; when it is back to room temperature, it should be flat enough for dry mounting.

Bowing of the mounted print is due to one layer (it can be either print or mount) changing size with respect to the other; depending on relative humidity, any of a number of scenarios can play out. If the mount is damp, and dries after coming out of the press, the result will be bowing away from the print; if the print is damp going into the press, the bow will develop in the opposite direction. Furthermore, the assemblage can be flat at the time of mounting (particularly if you dry the board in the press before mounting, as some folks recommend) and develop a bow later because reabsorption of moisture causes the elements to expand to different extents.

Allowing the prints and mounts to come to the same moisture equilibrium for a few days, and then minimizing the time/temperature during mounting, may help.

You mentioned Seal drymount tissue (MT5, possibly?), 200 F and four minutes: Seal (now Bienfang) Archival mount, 150--175 F, and two minutes should make life a bit easier. When the mounted print comes out of the press, immediately flatten it on cool surface (there are special plates made for this, but you can also just use your hands) so that it doesn't "set" a curved shape.

If you have to deal with really severe humidity changes, the classic solution is to dry-mount a "dummy" print of the same kind of paper on the back of the board; the resulting sandwich is balanced, and much more resistant to the effects of humidity change.

Good luck; others would probably like to know how you solve the problem.

Mount boards and the print need to be at the same relative humidity at the time of mounting. Even then any change in humidity will expand the mount more than the print resulting in curling.

The dummy print or countermount is the cure. Or use photo corners and learn to dry the prints flat. Corners allow the print and board to expand at different rates. A linen tape hinge at the top will accomplish the same thing.

Herb -

A couple of suggestions:

1. Place the print and the board on which it will be mounted, but without the mounting tissue, into the heated dry mount press, and warm them both for a minute. Take them out, and set them aside in the work space for a few minutes to cool. The fact that the board and the print have been elevated to the same temperature, and then allowed to cool together in the same environment, means that the humidity levels in the board and print will be stabilized at the same point prior to mounting.

2. After tacking the tissue to the print, trimming the print, and then tacking the tissue to the board, place them in the dry mount press. I set my press for 185 degrees and cook for 1.5 minutes. Then, take out the print/mount andwich, and allow it to cool, face down, on a clean table with a weight on top. I use a sheet of particle board with formica on one face.

This will result is prints that are about as flat as they can ever be.

The biggest reason for mounted print 'warping' (cupping) is that the virgin mounting board was not curred, by drying the latent moisture out of it BEFORE you attempt to mount a print.

Take the fresh dry mount board and put it in the 'hot' press for two to three minutes on each side, under pressure, before you attempt to mount a print on it. Easy, simple...works wonders.

If you really want super flat, mount kraft paper on the other side opposite the print...using the same technique of 'drying- out' the new mount board.

I agree with Richard...also be aware that if the press is too hot, the tissue will melt and the glue will be soaked in the board instead of staying between the print and the board...

You need to let the board cool down flattened under pressure. When you let it cool to 150, that is when the drymount adhesive shrank, making the board curl towards the side with the adhesive on it. You should never let it get the chance to shrink. Place a heavy piece of glass on top of it on the counter as quickly as you can when you take it out of the press. If the mounted photo cools down flattened under pressure, it will stay flat. That first minute out of the heat press makes all the difference.

Agreeing with all of the above suggestions, and adding to Craig's suggestion, after removing the print from the press I immediately roll the print with a rubber roller for 30 seconds or so during the cool down. I place 4 ply over the print for protection while rolling. This is with the archival tissue previously mentioned with a 90 second press time at 200 F. This works as well for the single weight Azo so weight is not an issue. Try to keep the press time to a minimum, four minutes is far too long. Good luck.

Dry mounting is especially tricky in a seasonal damp climate. My board comes from an un-heated warehouse, and in winter I know, despite its sealed outer packing, that it will contain so much moisture. My little trick for de-cupping the board is to spray water on the back with a plant mister after I've stuck a print down and when the board has cooled. I then place it on a surface, print side down and rub the droplets in evenly. I reckon this replaces lost moisture.
Some board cups no matter how much effort is put in to prevent it happening, and re-introducing moisture cures it.