Chromaline Exposure Calculator – Accurate Exposure Testing Tool for Screen Printing

Two calculators in one

The Chromaline exposure calculator doubles as a basic Step Test and a One Step Calculator, so you can test whichever emulsion chemistry you run.

One Step side for diazo and dual-cure

The left side has a special filter and is meant for diazo and dual-cure based emulsions. You read the line resolution targets on the developed stencil and apply a formula to get the correct exposure time.

Step Test side for photopolymer

The right side is meant for photopolymer emulsions. You make a series of progressively longer exposures on one screen and pick the image that looks best.

Three quality checks

Chromaline describes it as helping determine correct exposure time, run a print quality check, and test halftone quality.

Confirm your result

After calculating on the One Step side, Chromaline's instructions say to make a new stencil of the calculator at the calculated time to confirm the result.

One Step (left side): diazo and dual-cure

Place the calculator on the coated screen with the film's emulsion side in direct contact with the screen emulsion. The small filter must not touch the screen emulsion. Expose for twice the time you estimate is correct for your UV lamp and record it as the TEST EXPOSURE TIME. Develop the screen and dry it as normal, because wet screens are swollen and misleading. Pick the clearest, sharpest pair of line resolution targets and record the number between them.

The One Step formula

Best Target Number x Test Exposure Time = Correct Exposure Time. Chromaline's example: 0.50 x 2 minutes = 1 minute.

Step Test (right side): photopolymer

Tape the calculator emulsion-side against the coated screen. Expose for a base time you estimate. Then cover image #2 through #5 with black UV-opaque paper and expose again for an added time, leaving the calculator taped on. Move the paper down a step and repeat. In Chromaline's example (30 s base, 10 s added per step), you end up with exposures of 30 s (#5), 40 s (#4), 50 s (#3), 60 s (#2) and 70 s (#1). Develop, then select the image that looks best.

Reading Step Test results

Chromaline's example: if #4 looks best, 40 seconds is your exposure. If all the images are closed up, redo the test at a shorter base time.

Why test exposure at all

Chromaline states that at least 90% of stencil failures can be traced back to exposure times.

Manufacturer times are only a guide

Chromaline says exposure times can at best be suggested by manufacturers. Actual times vary with equipment, emulsion, mesh, coating technique and other shop conditions. It also says tests must be run regularly to confirm your times haven't changed with screen room conditions.

Signs of underexposure

Chromaline says a slimy stencil, or color coming off on your finger, means the screen is underexposed. Its troubleshooting guide lists underexposure as a cause of pinholes and points to the Exposure Calculator for finding proper exposure time and light source performance.

Lamp distance affects time

Chromaline states that as lamp distance increases, exposure time increases in proportion to the distance squared.

Light source range

Chromaline says all its emulsions (dual-cure, diazo and pure photopolymer) respond best to UV light in the 350-420 nm range.

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