Tuesday, March 03, 2009

Photopolymer Plates Part Two:  How to use a Stouffer Gage

In order to determine how long an exposure should be, the printing industry standard is the Stouffer Gauge. This is a piece of continuous tone film that is 1/2” x 5”. The first step shown is #2 which is a light grey, progressing up to #21 which is a very saturated black. Photopolymer plates each have a target exposure on the Stouffer Gauge for optimal results. For a 145HSB plate from Boxcar Press, the 21-step exposure scale target is 19-20. The way to determine your length of exposure is to cut a 1/2“x5” piece of photopolymer, weight the film strip ink side down under glass, then expose your strip at an initial time. Wash your plate out after your exposure under tepid water using a soft brush. The image will be solid up to a certain number on the scale, then it will start to have pinholes and disappear entirely. If 1 hour yields a result of 3 and your goal is 12, you have to multiply by 4.0, so you would need to expose for 12 hours.

Rules for Increasing Exposure Time:
To increase by 1 Step, multiply original exposure by 1.4
2 STEPS X2.0
3 STEPS X2.8
4 STEPS X4.0

This is the answer to getting consistent great results with your photopolymer plates. Check back for Part 3 soon!

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