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Cmyk Separation - What Colour Tones

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Old June 23rd, 2007, 05:46 AM   #1 (permalink)
Bruce Robertson Bruce Robertson is offline
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Post Cmyk Separation - What Colour Tones

Hi.

Can anyone please teach me something. If I design and produce colour separations in Photoshop (or Corel for that matter) (but maybe best stick with Photoshop for this) for screen printing, how do I know what tone of cyan, magenta, and yellow ink to use?
When I have been trawling around trying to find an answer to this it all gets hugely complicated. I've learned a lot about the process of producing halftone screens for bitmap type images from the web and various books but I'm unclear as to how I know what tone of colour Photoshop is thinking about when it says CMYK (or RGB for that matter). There are lots of shades of blue and red that could be called cyan or magenta. If it is thinking about Pantone colours - how do I get the number?

Also, (maybe pushing my luck here I think), has anybody tried printing in oil paint on canvas?

Here's hoping. Thanks very much,

Bruce.
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Old June 23rd, 2007, 08:07 AM   #2 (permalink)
Greg hamrick Greg hamrick is offline
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Default Re: Cmyk Separation - What Colour Tones

Hi Bruce,
The tones of ink you use for process printing are already mixed. Wilflex, to me, makes the best process inks, followed closely by, "if not just as good", Rutland and Union.
The inks are semi-transparent so that light passes through them and bounces back off the white underneath making you think you see color. So there are no "real" colors, just half-tones set at different angles. For instance: Cyan and Black may be preset at 45 degrees and yellow at 15 and magenta at 65. Just let Corel or Photoshop use their calibration with the printers settings, all you need do is worry about the artwork looking good.
Stay away from RGB, as separating four-color-process in that format will give you a slight off-color. Convert it to CMYK before making your separations so that the outcome is as close to the artworks color as possible. Panatone colors are simply solid color, but can be broke down and reproduced by printing four-color-process.
You mentioned just sticking with Photoshop, I have used both programs for separations and found that Corel Draw works the best for screenprinting. Some will argue, but it just comes down to the users preference. So use what you feel comfortable with.
As far as printing oil on canvas, I don't know if it can be done. The oils would have to be thinned down to be semi-transparent and the surface of the canvas is rough. The uneven surface will cause ink build-up in the valleys and dot gain on the ridges. So it would be impossible to get the colours right. The prints sold in stores done that way are printed on flat stock then pressed on a mold to give it that canvas look.

Hope this helps.....................
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Old June 23rd, 2007, 09:05 AM   #3 (permalink)
Bruce Robertson Bruce Robertson is offline
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Default Re: Cmyk Separation - What Colour Tones

Greg,
Thanks you very much for that speedy and useful reply. I understand what you mean about the pooling in the canvas and the consequent dot gain.
I'll go and have a look at colours on the web at Wilflex, Rutland and Union now.
Many thanks.
Bruce
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