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TMOGUL · August 17th, 2007

is there a such thing as over burning a screen and what happens when a screen is exposed longer than usual, and is there a remedy for washing out over exposed screens to retain the image or do i have to re-coat the screen and start over

TeddyRocky · August 17th, 2007

Quote:

Originally Posted by TMOGUL


	is there a such thing as over burning a screen and what happens when a screen is exposed longer than usual, and is there a remedy for washing out over exposed screens to retain the image or do i have to re-coat the screen and start over

Yes there is such a thing as over exposing a screen. There is no remedy for it really, but you may try using a pressure washer with minimal pressure to try knocking out the stencil, but it is very likely you won't get a clean stencil or if any. Over exposing causes emulsion in the stencil to actually expose as well, causing it to be very difficult to blow out. You will have to reclaim the screen, and start over again.

TMOGUL · August 17th, 2007

how long is burn time for standard exposure unit...thanks for the response too!

Fluid · August 17th, 2007

Quote:


	how long is burn time for standard exposure unit...thanks for the response too!

There is no standard burn time. Too many variables come into play.
Type of exposure unit. type of bulbs, how old the bulbs are, type of emulsion, age of emulsion, type of film, vellum being used to burn art, screen mesh, etc.

What exactly are the issues you are having?

State What type of unit are you using, what type of bulbs, what type of emulsion and screen mesh

RichardGreaves · August 17th, 2007

There are two goals with exposure.

Crosslink the emulsion with sensitizer so it is durable and stays in the mesh. Crosslink all the sensitizer so when you want to reclaim the mesh and remove the stencil, it falls off the mesh with little effort because stencil remover attacks the crosslinks.

But if you expose long enough to do all that crosslinking, you may also have too much UV light undercutting your positive and bouncing around in the mesh so that your fines lines close up and ink won't transfer through the mesh.

It's not really over exposure that is the problem, it's that exposure can change the size of your image. You can prevent this with faster exposing stencils, stronger, single point, calibrated metal halide lamps so the work of exposure is done quickly, before the light scatter gets you!

Here is one thread about this we have posted in the past:
The longer the exposure time the better?

Search this forum for light scatter and over exposure, or just plain exposure.

The screen is your printing tool, and learning to JUDGE exposure is the most important skill you need.

ryonet · August 17th, 2007

yes it just depends on how long you over burned

mpls_t · August 20th, 2007

For a beginner making t-shirts, would it be safer to overburn than to underburn?

RichardGreaves · August 21st, 2007

Quote:

Originally Posted by mpls_t


	For a beginner making t-shirts, would it be safer to overburn than to underburn?

Yes.

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airraidapparel · August 22nd, 2007

You might want to get an emulsion calculator so you can target your precise exposure times. As everyone else has said, exposure times vary by emulsion type, light, how long it's been sitting and if any light has hit it before it was exposed.

I've been screen printing for a long time, used a ton of different emulsions and found that my diazo-core emulsion exposes best for 10 minutes on the dot. I then pre-wash the screen with a spray bottle of water and a damp cloth. I've found that lightly soaking and scrubbing the substrate (side that hits the shirt) side before I pressure wash it really helps get fine detail out.

Hope that helps!

Drew