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  1. #1
    Mat Pringle's Avatar

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    Default Exposure issue/loss of detail problem

    Hi all,

    I'm new here - been meaning to introduce myself but couldn't find a suitable place so I'll cut to the chase and get straight into my current print dilemma.

    I'm an illustrator and print-maker based in South London, UK. I used to work out of a shared print studio with a fancy vacuum exposure unit but have long since left to make my own hotch-potch set up.

    I recently got a new screen and a new halogen work lamp (x2 500w) for exposing as well as a some new photo emulsion. Up till then I was using four year old emulsion and wondering why it was causing me so much grief to expose with!

    So I did my first screen this week. In the past I used to only coat one side of the screen but for a change decided to coat both sides as recommended by some. Any thoughts on this?

    I exposed the screen with the lamps 25" above for 25 minutes. In hind sight this may have been too long. Can exposing a screen for too long lead to loss in detail? The picture below shows the problem - the trace with the negative on is crisp and clean (although there is some slight pixelation which annoyed me but that's a different story!) but as you can see the in the print below there has been some loss of detail.



    Initially when I washed the screen out I was stoked with what looked like a super clean exposure and in fact I didn't really notice the loss in detail (specifically on the lettering) until I'd done a run of prints. Part of the issue is I've gone with a computer font - usually I do my own lettering but I felt it suited the design. Hand drawn lettering is more forgiving in screen-printing in my experience...

    It's not that bad in the scheme of things - the picture above is fairly close up - but I'm a bit anal so it's bugging me and I want to get the next layer crisper and cleaner if possible as that should tighten up the whole thing.

    Anyway I'm banging on a bit. If anyone made it this far could you let me know what I'm doing wrong?

    Exposure time? (would 15-20 minutes make for a cleaner/tighter exposure?)
    The two lamps point in slightly different directions - could this lead to blurring?
    Are they too far away? They were also a slight angle to the screen and not 100% over the top - would this be an issue?
    Double coating - yay or nay?

    Any help would be most welcome!

  2. #2

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    What mesh count fabric are you using, and in lieu of a vacuum, how are you compressing the positive to the mesh when burning?

  3. #3
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    Andymac's Avatar

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    yeah, you can't just say - 'it's the exposure time'.

    mesh? white, yellow, thread count

    physical edge of stencil is shit? or the edge of the print? there is a difference.

    vacuum or no on print setup? printing a big reverse with no vac will give you blurred images - not the fault of the stencil

    A double coating front and back is how it should be done. the thicker emulsion will increase time, but a quick check to see if you are exposed properly is to rub the top side (squeegee side) after your washout - is it still sticky/slimey? if it is it is underexposed.

    If it is hard (not sticky) it is exposed through, then check your film edge with your stencil edge. If it is the same as the film, you are exposed ok. if it is smaller than the film (the opening) you are either (a) over exposing, (b) getting undercutting from light going in at an angle, (c) getting light under because you have no compression of the film to the emulsion - it has to be tight or the light will undercut.

    more pictures would help.

    were the first prints better than the last? I would blame your printing/flooding technique.
    Andymac

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

    Todo es empezar.

  4. #4
    Mat Pringle's Avatar

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    Quote Originally Posted by edwardo_machino View Post
    What mesh count fabric are you using, and in lieu of a vacuum, how are you compressing the positive to the mesh when burning?
    The mesh count is 90T and I'm using a thin sheet of glass to compress the positive to the mesh.

  5. #5
    Mat Pringle's Avatar

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    Hi Andy,

    Sorry - I thought I included a lot of detail but apparently not!

    The mesh is yellow 90T.

    I think the edge of the print on the stencil is a bit pixelated but I'm not totally sure what you mean - and as pixelated as it is, it's still much cleaner than the prints as you can see in the pics.

    I have no vacuum on print set up. By 'big reverse' do you mean like in this case where I'm pulling a block of colour and the lettering is left blank? Sorry again - I'm not up-to-speed on my terminology but I do really appreciate the help.

    That's good to know on the double coating and exposure - thanks. I washed out the screen earlier today so can't double check against the negative as you recommend but will be sure to do it next time. I remember thinking the exposed screen looked really clean/sharp after washing it out so I suspect I had exposed it pretty much correctly.

    To be honest the first prints were as good as the last. The only thing I did notice to get worse through printing was the tiniest amount of leakage through the a couple of areas that should have been fully blocked - I just used some sticky tape to cover the few bits up where this occurred.

    I will be sure to take more pictures for the next print run and also follow your guidelines on checking to see if the screen is exposed properly.

    I really appreciate your help - thanks!

    From what you've said I suspect it's probably mostly to do with "printing a big reverse with no vac will give you blurred images".

    What's the best way around this bar getting a vacuum? Sticky spray?

  6. #6
    squeegeethree's Avatar

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    If this is the first time the screen has been used it is prone to doing exactly what you depicted. Also since you aren't using a vacuum exposer I would suggest you experiment with clear film instead that frost Vellum.

  7. #7
    Mat Pringle's Avatar

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    Quote Originally Posted by squeegeethree View Post
    If this is the first time the screen has been used it is prone to doing exactly what you depicted. Also since you aren't using a vacuum exposer I would suggest you experiment with clear film instead that frost Vellum.
    It is the first time I have used the screen yes - good to know - thanks.

    I usually get my negatives printed on acetate rather than trace but I'm currently living in the arse-end of nowhere so I had limited access to printers. Thanks again.

  8. #8
    Hrabovsky's Avatar

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    1) Poor contact between positive+mesh
    2) Jacked lamp angles
    3) Vellum light leak
    4) An enthusiastic washout

    But I don't know. The KO text lost all the serifs and counters.

    Andymac knows WTF is up.

    I tried to register a screen I'd burned backward this morning for ten minutes.

    Oh yeah, name your cheese, go premium, so on and so forth….
    Last edited by Hrabovsky; 10-25-2011 at 12:44 PM. Reason: dorks

  9. #9
    Mat Pringle's Avatar

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    Quote Originally Posted by Hrabovsky View Post
    Oh yeah, name your cheese, go premium, so on and so forth….
    Eh?


    I think you may have some good points too. By enthusiastic washout do you mean I've gone at it too hard?

  10. #10
    squeegeethree's Avatar

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    You need to name your favorite cheese at this point. It's a right of passage.

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