I've been using standard screen supplies t-1000 photopolymer emulsion with a vacum light box exposure unit for the past couple months. I've been putting the images on regular transparency paper and exposing the 110 mesh for around 3 min and everything has been working perfect. Last night I put some images on vellum and tried burning today and had no success with it at all. Do I have to drasticaly increase the exposure time with the vellum? I'd really appreciate any help that anyone can give me. Thanks
Exposure time help please
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yes you do. since the vellum is not 100% tranparent like a transparency you have to expend your exposure time. my opinion is to stay with the transparencys. i get mine really cheap from Binding Machine - Laminating Pouch - Filmsourceinc.net - Roll Laminators - Laminators - Pouch Laminator - Binding Machines
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vellum sucks. you need a very high powered light and exposure meter to figure out the timing. i could not even guess what i would expose it at
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You don't say whether or not the image is washing out, but since everyone else seems to assume you're underexposing when using the vellum, why not try it a double your usual exposure? If that won't wash out, drop it down to 4-1/2 minutes. If it all washes out, go to 12 minutes. The idea of doubling or halving times is one used in photography and brings an element of consistency to testing, rather than just picking a number at random, and when that doesn't work, pull another one out of thin air.
You should really invest in an exposure testing sheet. There are some free ones, but a good one is the one made by Chromaline. It will get you in the ballpark with one exposure test. You'll need to run exposure tests every time you change emulsions anyway, so the test sheet just makes the job easier. Technically, you should also do it for each mesh count, but what I've done with success is do my tests on a 195 or 230 mesh, which is in the middle range of mesh counts I use, and then extrapolate what should be a good exposure time for mesh counts above and below that. I then fine-tune them base on the amount of unexposed emulsion left on the squeegie side of the mesh at washout time.
You should really invest in an exposure testing sheet. There are some free ones, but a good one is the one made by Chromaline. It will get you in the ballpark with one exposure test. You'll need to run exposure tests every time you change emulsions anyway, so the test sheet just makes the job easier. Technically, you should also do it for each mesh count, but what I've done with success is do my tests on a 195 or 230 mesh, which is in the middle range of mesh counts I use, and then extrapolate what should be a good exposure time for mesh counts above and below that. I then fine-tune them base on the amount of unexposed emulsion left on the squeegie side of the mesh at washout time.
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