My apologies, I should have provided more detail straight away. Please see the image, it shows the dimple in reflected skylight. The dimple is gentle and only visible in such lighting.
Originally Posted by Robert Hall
I always pre-dry the mount board (1 minute, with pressure) and separately the print (1 min, no pressure except a gentle 5s squeeze at the beginning). I predry them both between three larger, already warmed and predried mount boards (two above, one below). Trimming and mounting is completed within 20 minutes.
This issue does not happen when using (a slightly thinner) Ilford Gallerie paper but only with Ilford MGIV FB glossy. The size of the trimmed print is about 11" x 15". The print is trimmed together with the tissue to their exact size on a Rotatrim, after the tissue had been tacked to the print in one place using a tacking iron. (It is then tacked in another spot to the board, creating a "Z" tack, as recommended by Hotpress, the makers of the tissue.)
The tissue is Hotpress Unimount Classic, a fairly popular make in this part of the world, I gather. It is the more traditional type which creates the bond when hot, not on cooling down like Buffermount etc.
The mount board is Silverprint's Conservation 4-ply (1.5mm) mount board, 16 x 20". The protective 3 sheets (one below and two above) are also the same boards but 20 x 24".
The platen is 20 x 23" in size on this Bogen (Technal) 560 press.
I am not sure what the temperature accuracy is as I have no confidence about the position of the temperature knob. It suggests that the temperature should be between 104 and 121 C (220 and 249 F), but I feel it is actually lower than that. Pressing with lower temperature settings caused corners to separate when bending finished and mounted prints, at the current temperature setting they seem to have better adhesion but they still occasionally delaminate when bending them outwards (repressing seems to fix that issue).
The pressing time is 3.5 mins (shorter times led to corner separation when bending). The "project" is arranged as, from the bottom press foampad: 1 large (20x24") 4-ply prewarmed mountboard, the actual 16x20" 4-ply (1.5mm) mountboard, 11x15" tissue, 11x15" MGIV FB print, another two 20x24" pre-warmed 4-ply mount boards, hot top platen.
It is difficult for me to describe the pressure, but it is not the maximum I could exert, perhaps 60-70% of the max possible. If I were to put my fingers between the platen and the foam, without the additional 3 mountboards, and close the press (cold naturally) the pressure is significant but perfectly bearable.
Please note that all of the above settings used to work quite well with a different brand of mount board and they continue to work well when using Gallerie FB paper, but not with MGIV FB.
I would be grateful for any suggestions you may have. More pressure, more/less time, higher/lower temp...? Thank you.