Screen Printing Forum

last night i exposed two screens both from the same emulsion, both printed form the same printer and computer, exposed for the same time.
one came put perfect, the other did not come out. it looked like it worked but wouldn't wash out all the way and had no defined edges where it did wash out.
so i started over today, it didn't burn in exactly the same way! so could it be my positive? but i printed exactly like the one that did work? is it possible my screen is messed up somehow?
Thanks if anyone can help me.

Are you using a vacuum frame, could be that you're getting undercutting by light.

what is a vaccum frame? i dont know, i did exactly the same thing to both screens one came out fine one didnt.
i tried to do it twice and teh second time it burned in exactly the same way.
same printer, same transparency film same everything except design, but the one that worked was far more detailed than the messed up one.

i hope someone can help me i am losing it!
i tried again today to expose this screen some of the words came out and some didn't. i did it for 5 min instead of 7.
my lights are all on in the exposure unit, my weight is flat, my emulsion is even.
maybe it's still too long? but again the other screen i did the other night along with this one came out perfect.
same emulsion same everything! its absolutely maddening. could there be something wrong with the screen?

If you don't have VERY good contact between your positive and your emulsion then light can leak under the mask and your halftones will be pants.
A vacuum frame sucks the air out and ensures that the film is right against the emulsion. From your answer I guess that you aren't using one...

Is the mesh count the same on the screens? Also, is it the same color mesh? A yellow 195 mesh has a different burn time than a white 195. A lower mesh count, 110, has a different burn time than a 156. There are quite a few variables. You can an exposure calculator or step-wedge test from your local supplier. These are an invaluable tool to have around. Once you find the perfect burn time for each type of screen you have keep a cheat sheet posted near your exposure unit.

It is possible that the screen wasnt dried properly or somehow got exposed to light before you were ready to use it, therefore was partially exposed before use. There is just a ton of reasons, it is really hard to pinpoint one specific cause.

Sounds like the one positive that didn't burn well seems to be lighter or not as black as the other one that burned fine.