To me, correct exposure means cross-linking all the sensitizer (hardening the stencil), so it won't dissolve with water and (contrary to instinct) will reclaim easily. UV energy has to move all the way through the stencil from the bottom. We can't flip it like a steak.
Low UV energy doesn't penetrate well, and when the inside of the screen isn't hardened/cured completely it still dissolves with water. Multiple fluorescent lamps, designed low resolution, large areas like signs don't make halftones easy.
No matter what UV source you have, at the edges, UV energy strikes the stencil at an angle. In addition, light scatters when it hits at an angle and is beyond the control of your positive. Scattered, under cutting uncontrolled UV energy chokes some fine lines or halftone shapes.
Harmless plastisol is like salad dressing. We can get away with uncured stencils because there is no damage to be afraid of, but water-base or solvent ink attacks the raw inside and the screen breaks down. Of course, many printers are then furious when they cleanup with stronger than needed solvents that chemically bond the uncured stencil to the mesh making stencil removal impossible.
Calibration
If you make a positive with 30% dots and they get choked, and print a 20% dot on the shirt, you can anticipate and supply 40% dots on the positive, completely cure the stencil and print your goal of calibrated 30% final dots.
For the best results, you adjust for the conditions. If your dots are closing in, you are only doing half what must be done to get accurate prints with your underexposing shortcut.
Frog, can you make this a new thread?
