I too use release paper and acid free interleaving paper between the platen. I also turn the sandwich 180 around when 3/4's time has expired. I tack only on three corners. Cool under a metal plate and have not run into your situation. The prints are on FB paper and the mat board is 100% rag. However, I have been shying away from dry mounting and going to archival corners more frequently because if the board is damaged or develops climate stains with our high humidity the print is shot.
Rafal - If you have experienced uneven heating with a thin protective sheet, maybe your platen is not heating evenly??
Don't the tissues actually bond while they cool down? Try leaving the print between the glass a little longer.
I owe you an answer how to solve the egde-long dimple problem, even though it has been more than a year since I started this thread.
As I have attended John Sexton's excellent The Expressive Black and White Print workshop (my experience: http://rafal.net/2012/02/the-express...y-john-sexton/), a true gem was meeting his wife, Anne Larsen, who is a perfectionist when it comes to finishing prints, which includes dry-mounting, her primary technique of mounting. Her finish is faultless in every way...
Anne explained that the edge-long dimple was a problem affecting some papers, notably MGIV, which I use a lot. Perhaps it is to do with the very strong anti-curl features of this pleasantly stiff paper. Incidentally, I think the issue is also related to the size of the print, as at smaller (less than 12") sizes it happens less frequently. Anne's solution is to mount the print normally (see below for her approach), and then:
- Let the press cool down to about 80?C (ca. 175?F),
- Insert the already mounted print back into the press for a further 4 min or so, and apply full pressure.
Please note, that these instructions apply when using traditional tissues, such as Unimount or Colourmount, which adhere when hot. I am not sure, and I have not asked her, what would be the procedure with tissues that bond on cooling down, like Buffermount etc. As a philosophical aside, don't all tissues bond when they cool, difference being the temperature point?
All of this is in reference to a "normal" mounting procedure, which would be quite different for everyone, I suppose. So as a reference, this is what I observed as her approach, when mounting work using Colourmount tissue:
- The press (usual, mechanical) is set to a very, very hard level of pressure. There was no way I could even half-close it with my hand between the plattens, when cold.
- The bottom bed, which usually comprises foam over masonite, was used upside-down, with the foam below, acting as a spring, and the hard, masonite surface was on top, therefore under additional mount boards, which were placed under the mount board, that the print was being mounted to. I realise this contradicts the wisdom from the queen of mounting, Chris Paschke, as written in her handbook. But, it worked.
- Operating temperature was 93? C (200? F).
- There were two 4-ply (1.2 mm) boards under the print's own mat board, and so above the masonite.
- There was only 1 sheet of regular 4-ply mount board above the print and under the platten.
- She did not pre-dry mount boards (to my surprise, not sure if I could skip this step in Ireland's humid air).
- Print was pre-dried (and flattened) for 40 s under full pressure.
- Anne used a "cross" or X tacking pattern.
- The time in the press was 4 min.
- Out came perfection.
As a test, Anne recommended tearing a finished, mounted print, to see if the tissue adhered correctly to the print and the board. She did not feel there was a need to bend prints to check for corner adhesion, if you have tested the process a few times by tearing prints.
So, there you are. Now I need to try it all on my prints to see if I fix this recurring issue. By the way, there is every chance that I have written down my steps incorrectly, so please test, before relying... Any more feedback would be always very welcome.
I was dry-mounting today, and I have experienced the same problem. The solution described above has worked, and the edge-long dimple is gone. On another note, I have also moved closer to Anne's dry-mounting process, adding time, and pressure. The results are better, adhesion seems much better, but I still got an odd dimple—now rectified.