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  1. #1

    Default do yellow mesh screens take significantly longer to expose than white?

    in andy's book, it says that yellow takes longer to expose. i'm on a project that's deadline is super soon and i'm going to burn a screen with yellow mesh. my normal exposure times on my ghetto setup (500 watt photoflood at 2 feet for 25 minutes) with 195 white mesh screens. any suggestions?

  2. #2

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    yellow mesh takes half the time of exposure than white one.


    Quote Originally Posted by tonerj
    in andy's book, it says that yellow takes longer to expose. i'm on a project that's deadline is super soon and i'm going to burn a screen with yellow mesh. my normal exposure times on my ghetto setup (500 watt photoflood at 2 feet for 25 minutes) with 195 white mesh screens. any suggestions?

  3. #3

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    oh! god..thank you!

  4. #4
    bongalong's Avatar

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    the darker the mesh the longer your exposure time should be.

    it also depends on the mesh weave number, if its the same then i'd estimate the time would be about 1/4 longer.

    best is to do a test.

  5. #5

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    yeah, i'll give it a try now, seeing how the yellow mesh screen is 305

  6. #6
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    Andymac's Avatar

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    I would estimate 1/4 to double the time.

    White is way faster.

    Testing is the only way to know for sure, as the bulb for these types of light is not the same. have you removed the safety glass from the light, it kills UV.

    What exactly was not working when you go to wash out?

    Did you coat with a scoop coater?
    Andymac

    services www.squeegeeville.com
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    Todo es empezar.

  7. #7
    Evil Alice Corp's Avatar

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    my yellow screen mesh 195. I don't know the exact size of my screen.. the biggest size poster i can print is 12" by 18"

    i use a 250 watt photoflood BBA no.1 bulb
    and I expose it 17" away from the screen for about 25 minutes (about 8-10 minutes longer than it takes if i used a white mesh screen)
    so that works for me.

  8. #8

    Default

    Quote Originally Posted by Andymac
    I would estimate 1/4 to double the time.

    White is way faster.

    Testing is the only way to know for sure, as the bulb for these types of light is not the same. have you removed the safety glass from the light, it kills UV.

    What exactly was not working when you go to wash out?

    Did you coat with a scoop coater?
    safety glass from the light? do you mean the plasitc outside of the bulb? do you mean the plasitc outside of the bulb? my photoflood looks like a bigger version of a regular light bulb.

    when i washed out two screens i burned yesterday, the image details became visible but did not wash out. i could tell the didn't wash out because i held out the screen to the sun and i couldn't see through the lines. this was with a 305 yellow mesh screen. i tried to burn another screen (white, 195) and this exact same thing happenend during washout. it seemed to me that the emulsion could be old because it's been in and out of the fridge for months. it's ulano tx diazo. so i reclaimed/degreased the screens. the yellow mesh screen left more of a ghost image than usual, and i wondered if i overexposed.

    i don't know what's up, but i keep making really simple mistakes. i accidently added warm water to the diazo instead of cold like it said. and then i coated the screens again and left them overnight. then i remembered that you're supposed to wait a couple of hours before using the fresh emulsion. i checked them this morning, they were still obviously drying (some areas were bright green and wet) and the yellow mesh screen built up large areas of emulsion around the detail lines in the previous screen before. i decided that the yellow screen was a no go, and i was going to try to burn the other screen after school today so we'll see how that goes.

    i've been studying you're book like crazy just trying to figure out possible reasons why things are going wrong.

  9. #9
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    Andymac's Avatar

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    Give me a call 250 334-2598 we can figure it out.

    I thought you were using halogen? A halogen work lamp has a glass or plastic lense cover (not the bulb) get rid of that and the mesh cage.

    If the image showed but did not wash out, and the emulsion was hard and not slimey after you tried washing, then it is overexposed. I don't know what type of films you are using, but if you are exposing and the emulsion is hard but the image is not washing out, you may have been burning through the black on your positive if it is not dark enough to block the light. You can check this by taking a piece of rubylith or thick black paper and slipping it in a corner during your next exposure. It will wash out no matter what time you use. if it doesn't, something is wrong with the emulsion.
    if you are underexposed, the stencil will be all slimey or fall off the mesh during washout of the stencil.

    If you don't have an exposure calculator, then do a step wedge exposure with the fresh emulsion. If you do it once and determine your time, you should be able to determine a time that will work for your situation and materials as long as nothing changes substantially.

    keep trying.
    Andymac

    services www.squeegeeville.com
    equipment www.tmiscreenprinting.com

    Todo es empezar.

  10. #10
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    sorry i re-read your post re the photoflood.
    Andymac

    services www.squeegeeville.com
    equipment www.tmiscreenprinting.com

    Todo es empezar.

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