paper shrinking problem, don't know what to do any more ...
I have a big paper shriking problem since the beginning of my gum printing activities (I'm only a beginner) 1.5 years ago.
Classic problem I would say, after the first coating/developing/drying, once I try to re-register the transparency negative with the paper, I get about 1mm off for print 18cm in width (that's 0.04 " off for a 7 " print).
It's enough to make the print to look blurry after the second coating.
I tried pre-soaking the paper in different manners, tried pre-soaking and drying twice before the first coat, tryed let it soak a full day, no avail.
Tried different papers, BFK Rives, Somerset, Lanaquarelle, Montval, Hahnemuhle ... same issue more or less.
In the summer, when the temperature is about 25°C and 50% relative humidity, I get 1mm off on a 18cm print (A5) and in winter when it's more like 20°C and 60-70% humidity, its a bit better but still 1mm off for a 29cm print (A4). It doesnt even make sense to try bigger prints ...
What can I do about this ? Pre-shrink 10 times ? Print on wood instead of paper ?...
Thanks for your ideas & help in advance !
Not sure about your specific problem but at work we screen print onto polyester. We make sure that the material has done all of its shrinking before we start to print otherwise we would not be able to register print layers to each other.
Is it the paper itself which is shrinking? If so you should be able to come up with a process which will stabilise it before you start coating.
If it's the coating itself which is causing the shrinkage though, some sort of backing layer may be the only solution.
How do you do thie with polyester ? you mean you print on polyester or you bind the paper to polyester backing ?
We heat treat polyester at a slightly higher temperature than we are going to cure the ink at. It just goes down the drying line a couple of times before printing at about 5 degrees (C) above normal temperature.
Still pre-shrink, and:
- Try with a thinner gum/pigment emulsion mix. E.g. if your gum is 1+2 (gum+water), then use it as following: 1+1+0.5 (or 1) (gum/pigment+dichromate+water)... A too thick gum layer will end up shrinking paper proportionally to image. (Darker = thicker parts will shrink more...)
- Wait a little longer in the first layers (to let the paper dry to the touch), wait less (still has to be dry to the touch, though...) with the subsequent layers. (Check intermittently using the negative, and start to print when the images align perfectly...) Dampening the back of the paper with a moist sponge may help...
- If still everything fails, print the negatives for subsequent layers by shrinking the image according to the image size on paper. (Few trials will give you the shrinkage ratios on each step...) In other words; print the first negative, print the layer using it, measure the image size, and print the second negative to measure. (You'll workout the ratios, and be able to print all three or four negatives together later...) Pay extreme attention to the grain direction of the paper, though; shrink ratios vary according to grain direction...
- You may opt to affix the paper on a dimensionally stable support using removable dry mount tissue such as this one. But you need a dry mount press to do that... (This is Keith Taylor's method, mentioned here.)
Hope this helps,
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Thak you for this explanation Loris !
Yes i'm using 1+2 gum. I'll try with more water, but I may be mistaken but I have the feeling that it will only make the layer less pigment-dense (hence more layers needed) and take more time to dry. How could this affect the shrinking ?
For the second part, you mean to print first layers when the coating is extra dry, and the next ones when the paper is still a bit damp on the back ? (not fully skrinked to dry size)
I didn't think of making multiple negatives, but yes it seems to be the easiest option if the shrinking is consistent.
I have read this method already a few months ago but do not have such kind of hardware ...
Do you have "The Book of Alternative Photographic Processes" by Christopher James? I believe it lists a few different sizing formulas to try if plain water isn't working for you.
"Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."
- Rob Tyner (1944 - 1991)
Yes, the water will thin the emulsion, but that may work/help if you're currently printing an unnecessarily thick layer. The thicker the layers are, the more shrinks the paper. (Proportional to image that is - look at the back of the print, you'll probably see the embossed image...)
I don't mean extra dry, but considerably drier than the subsequent layers. E.g. if you're waiting 30 minutes before printing, wait 10-15 for the first layers, then more for the next ones... And if the paper shrinks too much, you can always slightly moisten (not wetting! just moistening...) the back to relax the fibers.
A good sizing helps in stabilizing paper strenght. Do you size after pre-shrinking? (If not, lay a hardened 3-4% gelatin sizing before the first layer.)
Also, print the light colors (yellow / magenta) first. The paper usually doesn't change dimension much after the first couple of layers... Since the dark / contrasty content (cyan / blue / black) will be put on paper after this stage, you won't notice much blurring etc...
Try to always hang the sheets from the same corners when drying, especially big prints.