« TechNotes

Preshrinking paper for multi-layer gum printing

Background
I've seen comments many times that paper needs to be preshrunk in hot water to minimize further shrinking during the printing process. I've been soaking my paper in hot tap water for 30 minutes, but I haven't found this to be very effective, so I thought maybe I should be using hotter water. I did some testing to see what effect the water temperature might have on the amount of shrinking.
 
The Materials
The paper I was working with was white Rives BFK, 250gsm. I used 11" x 15" sheets torn from 22" x 30" sheets.
 
The Testing
I tried soaking at three water temperatures in deep tubs of water. All of the sheets were agitated every 5 minutes for a total of 30 minutes and hung to dry after soaking:
1. Soak in cold tap water (68o F).
2. Soak in hot tap water (116o F). Final temp after 30 minutes was 87o F.
3. Soak in very hot water (136o F). Final temp after 30 minutes was 116o F.
Note: Water had to be heated on the stove for this test, and exposure to water at 133o F for 15 seconds can cause third degree burns. I found that a pair of heavy rubber gloves was necessary to allow me to get my hands in the water.
 
Before soaking, I put small pencil marks on the edges of each sheet, 260 mm (about 10 inches) apart on the short side and 360 mm (about 14 inches) apart on the long side. After soaking, I could then remeasure the distance between the marks to determine the amount of shrinking. I used two sheets for each test. After soaking and drying, I flattened the sheets in a drymount press before remeasuring.
 
The Results
I remeasured the final distance between the marks on each sheet:
 
cold tap water
sheet 1: 358.5 mm x 259.5 mm
sheet 2: 358 mm x 259.5 mm
 
hot tap water
sheet 1: 358 mm x 259.5 mm
sheet 2: 358 mm x 259.5 mm
 
very hot water
sheet 1: 358 mm x 259.5 mm
sheet 2: 358 mm x 259.5 mm
 
My Conclusions
1. The temperature of the presoak had no significant impact on the amount of shrinking (cold water was just as effective, and really hot water was no more effective) and

2. The amount of shrinking was much less than I had anticipated (and possibly not worth the trouble). Final dimensions in all cases were approximately 99.4% of the original length on the long dimension and 99.8% on the short dimension.