# How long to expose using the sun?



## tdh646 (Jan 28, 2009)

I'm in the San Francisco bay and it's nice a sunny outside. Its a bit cool though (about 55). I want to try exposing a screen to the sun but wanted to know how long it should be left out for. Ive done it this method a long time ago while taking a class in high school but don't remember how long I left it out.

Any takers?


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## PositiveDave (Dec 1, 2008)

January, England - about four days.


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## mrvixx (Jan 13, 2009)

on a clear day you can try 5-15 mins. sometimes less


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## RichardGreaves (Nov 7, 2006)

Every day, every hour, every emulsion & coating thickness is different. Even in California.



Read:
http://www.t-shirtforums.com/screen-printing/t19817.html#post121127

Learn to measure UV energy for your stencil with a US$10 21 step scale. You can measure the sun with two sacrifice exposures using a Stouffer 21 Step Scale to measure the stencil hardness, then shoot your serious stencils.

Exposure FAQ Screen Making Products how to measure exposure
* Measuring UV Exposure*
It is the primary job of the screen maker to learn how to judge exposure. Invisible UV energy reacts with emulsion sensitizer and hardens the stencil so it won't dissolve with water and rinse down the drain. You block UV energy with a positive during exposure so the image area dissolves when you develop the stencil with water. 



Screen makers can *only expose one side of the stencil*, so it is important for the UV energy to _move through the stencil_, all the way to the back, where the squeegee blade will rub the stencil where it is weakest.


When the stencil doesn't hold in the mesh, it didn't get enough exposure. Start by checking the suggested exposure time on the product Technical Data Sheet. These *estimated* time charts are based on known* commercial screen printing UV light sources *on 305 mesh. .


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## Cortwrong (Mar 15, 2011)

This was exposed in the sun for 25 seconds.

Anything more than that for halftone images and you're risking losing detail due to over exposure. I have an old table in my back yard to which i attached a piece of plywood by two hinges. I then put a rail on the hinge end to hold the frame and my exposure glass kind of like an easel. I place the whole sandwich (glass/film/screen/black tee shirt blank covering a foam board) on the easel, covered with a dark bath towel, and rotate the table to wherever the sun is. I then lift the hinged easel to face the sun directly, uncover, time 25 seconds, recover and washout.

Cortwrong---Out


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