screen printing > Screen Making
Speaking of Underexposure
yorkie:
--- Quote from: DouglasGrigar on May 22, 2011, 12:18:39 AM ---Underexposure is the MAIN problem for new people in this industry, I find many of the suppliers promoting underexposure and it directly harms many of the new people in their early quest for efficient procedures an quality printing.
--- End quote ---
New people don't understand the value of a quality exposure system, but think that an inexpensive system will do as well. The same is true for a vacuum frame verses foam compression. And of course a timer is just as good as a light integrator.
Cheap units tend to have long exposure times, so it takes 10 minutes just to produce the underexposed screen with soft edges. Washout is inconsistent.
The need for especially dark film is a symptom of an out of control exposure process.
DouglasGrigar:
--- Quote from: yorkie on May 22, 2011, 10:49:49 PM ---
Cheap units tend to have long exposure times, so it takes 10 minutes just to produce the underexposed screen with soft edges. Washout is inconsistent.
The need for especially dark film is a symptom of an out of control exposure process.
--- End quote ---
I don’t know if I would call it out of control, I can show someone how to control that - it is a situation that needs direct and specific attention.
A positive with low D-min and very high D-max is a good thing regardless of the power of the exposing unit...
We had to ban the use of amber masking film and then Ruby masking film because of burn-through with a very high power MH system (one of the big guys that would take a 5x8 foot screen and would dim the lights when punched) we had a high quality SA wet bath roll feed image-setter (24”x300’ roll feed) silver based system that had beautiful positives later and were using silver film from a camera before that and had the quality positives to make up for the ban on masking films... Amber was easy to see and crap to shoot... ruby ended up as a pale contender to silver films...
yorkie:
Blasting through rubylith would be my definition of "overexposed".
squeezee:
I spent years formulating masking films for Autotype.
Amber actually has the highest uv density OD 4 +, Ruby was slightly lower.
I suspect that you weren't burning through the mask in the uv, an OD of 4 stops 99.99% of light at that wavelength, but that your bulb was putting out some visible wavelengths to which your screen was slightly sensitive. The Amber lets more visible light through than the Ruby.
RichardGreaves:
Douglas has a cool, interesting, one-of-a-kind story about a super powerful unknown lamp and a un-common, "high quality SA wet bath roll feed image-setter (24”x300’ roll feed) silver based system". This would be in the "Formula One" stratosphere of equipment, especially on "theshirtboard".
In Wisconsin, I knew a guy with a rocket powered car. His gas mileage was poor.
For the rest of us here on earth, 4.0-4.2 UV density masking films work very well, especially in this age of 1.6 UV density 'stock' ink jet positives where many art departments don't want to bother with increased UV density they can get from a US$500 RIP.
I've personally made more screens in the sign or flag business with masking film than most people have had hot dinners and I was the Ulano product manager that lead the program to kill AmberLITH because of poor sales. I was very sorry to see it go.
"Cheap" is usually mixed up with "Low energy". I would phrase an opacity statement differently than 'yorkie'. I encourage desire for controls, that's why I like to measure. More UV density is more control. I'm a silver film lover from the 1970's.
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