Re: Hardener after effects
Chromaline Magna/Cure UDC-2 is a very good 38% solids dual-cure emulsion with moderate water resistance. Completely exposed it should resist for thousands of images, no matter how many times you take the ink out.
A better choice from Chromaline would be an emulsion designed for water resistance like CP Tex - 42% solids, extremely durable, water resistant, designed for belt printers, yet still reclaimable if you use a pressure washer.
Of course, all water resistant stencils resist
water-based stencil remover, so they are traditionally all hard to reclaim.
CP TEX is about US$20 per gallon less expensive than UDC-2 - also sold in quarts for lower volume shops.
Measuring Stencil Hardness
You will get diazo color change with those stencils, but without a step wedge test positive, you can't really tell if you actually cross-linked all the sensitizer.
The best exposure test for stencil hardness is a US$10 Stouffer 21 Step Transmission Gray Scale.
http://www.stouffer.net/TransPage.htm#21-Step
A transmission gray scale is a small film positive with darker and darker filters next to each other in steps. This is a standard photographic darkroom test positive that's been used since the 1930's.
When you have one on the stencil as you expose, you'll get a simulation of 21 different exposures to the stencil and you get
visual feedback that shows how well your stencil is cured.
When you develop the stencil, areas that didn’t get enough exposure will dissolve with water and rinse down the drain. Aim for a minimum of a Solid Step 7 that adheres to the mesh and survives development. More exposure will make your stencil more durable and less will make the stencil less durable, but light scatter could start to choke fine lines or halftones.
The Thin Ice of Under Exposure
You might consider under exposing, but at the expense of a weak stencil on the inside - where the ink is.
Plastisol ink is like salad dressing when it comes to attacking a stencil, but water-based ink, (made of 80% water) is made of the stuff that dissolves un-cured stencil like the Wicked Witch of the West.
Once you know how to completely cure the stencil - then you can focus on how to get fine lines to print. That's when you worry about using an exposure calculator to calculate how to fatten your fine line art so it survives the choke of under cutting or light scatter.
Put one on an out-of-the-way edge of every screen you expose for the rest of your life.
