Clear film positives allow percent of the UV light to reach the stencil, where vellum allows only This amounts to a This two minute difference in exposure can cause the UV light to completely pass through the opaque areas of the film positive.
All light will bend and thus an over-exposed stencil will result in the light bending around the edges of the details in the film positive. Thin lines will be decreased or be completely obliterated. Utilizing the correct exposure time will lessen the loss. Also, assuring that details are sufficient for the mesh count used will achieve this goal.
The finest detail that one should attempt to print with a specific mesh count will be equal to the width of one mesh opening and two threads. The size of mesh openings and thread width, stated in microns, is readily available from all mesh manufacturers. If you made the film positive by hand double siding you should use a clear film positive with an opaque ink. If you printed or copied directly onto the transparency, try increasing the darkness of the image.
It is possible to use two copies sandwiched together, as long as the clarity of the minimum density areas are not affected. Reread the section on making positives for more information. Widespread over-exposure can also happen if you allow the photo emulsion to receive too much exposure. After the initial exposure move your art and sheet to the next section, covering the 4-minute section with a light safe sheet as well, you only want the 6-minute section exposed to your light source.
Expose this section for 6 minutes and follow this procedure until ALL 4 sections have been exposed at the times indicated. Wash out the screen as you normally would, completely wetting both sides the let it sit for a few minutes allowing the emulsion to soften your washout room should be yellow lit as well then spray softly again on both sides until you see your image washing out.
To determine the best exposure look for; edge definition and degree of unexposed emulsion on the squeegee side while washing out. Be aware on finer detail you may want to cut back time to maintain the details. This is nothing more than exposing the screen on the unit for 10 to 15 minutes or setting it in the sun for 5 minutes, why?
During your initial exposure your only trying to burn the image on a screen and maintain detail, post-hardening will ensure a strong, long lasting screen. Create your account Lost password? First name.
Last name. Company Name. If you are using new emulsion, it is best to mix it an hour or so in advance so that all the bubbles can disperse.
You can watch a video showing how to mix up your emulsion here. When coating your screen the best tool to use is a coating trough, failing that, I have often used an old credit card. The aim of coating screens is to fill all of the holes in the weave of the mesh, not to deposit a couple of mm on top of the mesh. Make sure your emulsion coat is even and that you coat and remove excess emulsion from both the inside and outside of the screen.
It is also important to wipe off any blobs around the edge. Dry the screen horizontally, printing side up somewhere dark. It is good practice to put some wedges blocks under the frame to allow the air to circulate. It is possible to speed this process up by using a fan on cold never warm but I have experienced more problems when drying this way. When the screen is completely dry you are ready to expose your screen. The next crucial part is the positive.
This should be printed on acetate and be very dark so that light cannot pass through the dark areas, you can test for this by placing the positive on a lightbox or holding up to a window. Some exposure units have lights below, others from above.
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