[pure-silver] Re: rc prints curling
----- Original Message ----- From: "John Bower" <john@xxxxxxxxxxxxxxxxx> 
To: "Silver Silver" <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, April 23, 2009 7:35 AM
Subject: [pure-silver] rc prints curling
Ever since I started printing (~8 years ago) my RC prints (Ilford Multigrade IV, pearl finish) develop a slight curl when drying (the corners turn up, so the print has a slight bowl shape). After rinsing for 3-4 minutes, I squeegee them on each side, then place them on fiberglass screens, and they always have the curl when dry. Why? Shouldn't RC prints dry perfectly flat? 
John Bower
Both prints and films curl for the same reason: the emulsion shrinks at a different rate than the support. Since RC support can not absorb water it is the emulsion side that is causing the curl. When gelatin dries it shrinks and expands again when it absorbs water from the air. I've found that mostly RC prints dry pretty flat but when it gets really dry here (was 7% two days ago) they curl so strongly that they will peel right off mounts if spray-on adhesive is used. Dry mount won't peel off but can actually curl cardboard mounts. I suppose the application of a humectant such as glycerine might help but anti print curling solutions are supposed to be a bad idea from the archival standpoint (can support fungus growth). I suspect steaming the emulsion side would take the curl out, at least temporarily. Fiber also curls because the emulsion shrinks faster than the support. The idea of drying on screens emulsion side down is to keep some moisture in the emulsion while allowing the support side to dry. I've never found this to work particularly well. Blotter books have a layer of non-absorbent material on one side again to prevent the emulsion side from drying out too fast. The only method I've ever found that gives me reasonably flat fiber prints is to treat them in a dry mounting press. That works well but should not be necessary for RC prints. 
    BTW I also dry RC by hanging it like film.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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