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What's the lowdown on halftones???

1256 Views 7 Replies 5 Participants Last post by  TYGERON, 
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Hey, guys!

I've been screenprinting for about a year now and I'm just now trying to complete a project for the first time with halftones. I'm trying to print an image that an artist friend of mine drew with a pencil. I was able to convert the image to halftones using PS bitmap feature and want to print it in black.

My output is set to 300dpi, frequency 20, angle 0, and shape is round. The image printed up really well and I'm pretty confident it'll turn out if I get everything else right.

My question, and please don't use terms like "moire" and "cross linked" because it will just further confuse me! I'm using a halogen (no vacuum blanket) for exposure with black foam underneath and weight on top. I have screens that are 110, 156, and 200. Does the exposure time change for halftones and which screen mesh should I use? I'm guessing 110 is too low.

Here's the original image before I converted it.

Thank you!

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R
exposure time will change depending on mesh count.

the LPI will determine the halftone dot sizes used when generating the pattern. what LPI are you using? if you're highest mesh count is 200 i would recommend 45lpi
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D
simple low down...

...you said you have 200 mesh. use that (i'd do 305 myself)
...coat with emulsion, 1 pass shirt side - 1 pass squeegee side.

...when you print your film, print at 40lpi (i can easily set this with my Accurip. at 305 mesh i myself print it at 55lpi)

...your exposure unit is fine. make sure you put good weight on top. exposure time you need to ball park it. usually it's few seconds lower than your 110 or 105 mesh artworks.

...document your settings from start to finish so you know where to go back and do adjustments later.

...you may not get it the first time. but the possibility of getting is the first time is very very high. :)
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You guys rock! Thank you :)
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Frequency is where you would set your lpi
20lpi is a very large halftone dot pattern and is visible to the eye from arms length when printed, usually not ideal. i wouldn't recommend going lower the 40lpi, even 40lpi i find the halftone dots to be too visible. Altho using a low lpi can generate a cool effect (sort of like pop art or mimic the look of an old print)
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TYGERON
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pacificthinktees said:
I've been screenprinting for about a year now and I'm just now trying to complete a project for the first time with halftones.
My question, and please don't use terms like "moire" and "cross linked" because it will just further confuse me!
Click to expand...
OK. I suggest you start with finding out what your ideal exposure time is by using a single step exposure calculator. You don't have to use an entire coated screen. You can coat an area just big enough for the calculator to cover. You can use the rest of the screen small areas at a time if you need to do it more than once. You'll get differing exposure times with different mesh counts and different color mesh. The 200 is probably dyed yellow(?).
"Moire" is the pattern created when the frequency of repeating patterns "clash". It happens anyway so what you want is "desireable" moire or a pleasing pattern. It's like when you hit 2 notes on a piano. If they are close you get harmonic dissonance. As they are separated by longer intervals, it sounds more pleasing or more harmonic.
There are angles (between dots and mesh) that create a more pleasing moire. Like 22.5 is one suggested angle to start. Before you burn the screen you can place the film over the uncoated mesh and see the pattern. As you turn it you can see the pattern change.
Halftones don't have to be on 305 mesh with 55 or 65 lpi. Depends on the look you want and other factors. Try starting with the 156 and work your way up to the 200.
The image on the left is a process print 156 mesh 42.5 line. The right one was 200 mesh 55 line 22.5° single pass on black.

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InkedApparel
...your exposure unit is fine. make sure you put good weight on top. exposure time you need to ball park it. usually it's few seconds lower than your 110 or 105 mesh artworks.
Click to expand...
this might be the best advice to give a new screen printer......because we all know that if your gonna ball park something....the exposure time is the perfect place to "ball park it"

lol.....hahahaha!

Inked
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TYGERON
InkedApparel said:
...because we all know that if your gonna ball park something....the exposure time is the perfect place to "ball park it"

lol.....hahahaha!

Inked
Click to expand...
You ain't right! :D
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