Screen Printing Forum

Hi everyone, im very new to this so please excuse the stupid q's

Ok I have my 1000w halogen on a frame and my screen is coated and in a light safe box drying over night, tomorrow night I plan to do a step wedge test, which if I understand correctly i cover the whole of the emulsion with paper and then slowly take some of it away in time intervals, is this right?

I know this is meant to help work out the exposure times, but what EXACTLY am i looking for when ive done it, ok say ive been doing a test from 1 min to 30 mins and every 5 mins I have taken some more of the paper away, what do I need to look for to know it was the right time, do I need to have an image going across it or is it just the emulsion? How will I know what segment is the right one?

Can I use water-based white ink on a black t-shirt? if so is there anything different I need to do compared to printing onto light material?

And lastly to top it off....

Im using an emulsion coater, how fast should I be coating the screen, sounds stupid I know but is it like a really fast swipe up the screen the again on the other side or should I take my time??

Thanks to anyone that can help me !

Jay

regarding the test.

Get some good film with small type and lines. make sure it is opaque. make sure you have enough to expose with your different steps. Make sure it is pressed tight to the screen during the exposure - are you using a vacuum blanket?

when you wash out, the underexposed areas will seem thin, in fact the way underexposed will come off the screens

where it is closer to the right time, the image will be crisp and only the type or image will washout. you will have a few steps that look like this

where it is overexposed, the type or fine lines will close in and not wash out easily. the stencil will be solid

-You need to wash the whole stencil well, washing out from the squeegee side (the side away from the light.

So the second thing you check for in the range where the image washed out good, is for a solid stencil - no pinholes, and here's the kicker - AFTER A THOUROUGH WASHOUT WITH SPRAY when there is no more to wash off, rub the surface of the stencil with your hand.

If it is slimey and some soft emulsion is on your fingers, this is still underexposed. You want to find the spot where the image is like the film, the stencil has no pinholes or is soft, and the surface after washout is solid, not slimey.

whatever the time was on that step, that's your time. don't be afraid to vary it a bit as you make more exposures, always hunt for the perfect stencil.

You want to print white ink on a shirt, use a 110 or 125 mesh, coat it out, then coat the bottom again after it is dry. A thick stencil on a coarse mesh will give you a higher ink deposit

thicker stencil = more time. white mesh is faster (1/2-1/3) exposing than yellow

coating speed... its' not a race, but smooth and steady - if you go to slow it will cause creases/flaws in the coat, or make it too thick.

hope that helps!