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Thread: Moire?

  1. #1
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    Default Moire?

    I've been searching the forums but can't seem to find the exact answer to the problem I'm having, so here goes. I am attempting to do tiny (45 - 50 lpi, I've tried a few combos) half tones on 305 mesh. I did find the suggestion on the forums to angle at 22 degrees, which gets rid of diamond patterns in the printout, which is great. However, I am getting this weird banding pattern when I burn the screen (see the pic). I know it's probably mesh interference, but can it be avoided through a different angle? Advice is appreciated!

    Last edited by jillustration; 03-05-2014 at 10:29 PM.

  2. #2
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    Also I did see this threadhttp://www.gigposters.com/forums/scr...ne-images.html but it was also suggested there to do 22 degrees, which is what mine is set to. Dunno if I should try another angle

  3. #3
    RichieGoodtimes's Avatar

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    Try 7 or 37.

    Also, what is the average tint percentage where moire is most apparent? You might want to try dropping that about 5% to open up the holes. That might eliminate the moire on its own. You might just be in that unfortunate mathematical vortex where the majority of your dots are landing on vertices, due to your angle and tint.

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    Richie- the banding is apparent throughout the whole gradient, but I will try lightening it up a bit and give both 7 and 37 a try. Thank you for the suggestions, I'll post photos later to let you know how it goes.

  5. #5
    squeegeethree's Avatar

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    You may also be exaggerating a little moire into a big one but not fully developing your screen. Go get a soft softscrub pad. The white kind (not the rough green or black ones). While developing your screen rub vigorously with the softscrub pad (both sides).
    We often seen moires from screens that aren't fully developed and this help out a lot.
    Looking at your photo, I also wonder what you are using for exposing your screens.
    There is no reason you should be getting a moire with a 45lpi on a 305. You're doing something wrong.

  6. #6
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    Of course I'm doing something wrong, I just don't know what yet . My exposure unit is a 1,000 watt metal halide lamp, suspended above the screen. I have a block of furniture foam covered with black felt, which I set the screen on (it fits inside the screen). On top of that, I lay a sheet of heavy non uv blocking glass to ensure the transparency is properly smooshed onto the screen. I know a vacuum exposure unit would be even better, but could that be the cause? Or under exposure perhaps? I'll try rubbing the screen with a white scrub pad too.

  7. #7
    squeegeethree's Avatar

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    Is the foam+felt thicker than the inside walls of the screen frame under the compression glass?

    If the image you posted was just a one color halftone with black on top then I'm pretty sure your coating, exposing and/or developing is the issue.

    If you have access to a light table you can spot a film to screen moire before it happens. Just tape your halftones film to the light table. Place the screen on top and turn the screen slowly and watch the moires form and leave. By doing this you can often isolate the moires at their tiniest and in places where they wont be seen. When you get it the way you want mark your screen with a pencil where the film goes and coat the screen. The pencil marks won't effect the emulsion and shooting.
    Last edited by squeegeethree; 03-06-2014 at 01:06 PM.

  8. #8
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    Yes, it is about an inch thicker. Even mushed down, the foam still holds shape pretty well and the screen doesn't touch the floor.

  9. #9
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    I'll take "not washed out fully" Alex.
    POSTER & STICKERS SCREEN PRINTING IN CANADA
    http://www.ironcladgraphics.com

  10. #10
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    Ok, so the first one shows 37 degrees on the left, 7 degrees on the right. I think Richie was spot on, these angles just look better. There is a tiny bit of moire with those 2 angles but it's barely noticeable. For reference, I burned the old transparency onto the same screen at 22 degrees, this is the bottom photo, and I did a test print. It's so odd that everyone else has good luck with 22 degrees and for me it doesn't work, but 7 and 37 work pretty well. I even rubbed both sides of the screen and spent extra time rinsing to be sure there was no emulsion left over, like squeegeethree said. I also tested a longer exposure time. Even though the moire pattern seemed a bit less, it was noticeably still there. Anyways, I think I solved my problem, thanks you guys!

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