Using the Y angle for the spot color will definitely cause a moiré. If you use a C, M, or K angle you will have no moiré. The dots will in essence print directly on top of the process dot, which will NEVER NEVER cause a moiré. A moiré happens when the angles the dots are on are different, unless they are 30º away so they can land between each other. Try it, Luc; you can see it in film negs even.
Peace!!
_mjnc
Last edited by MJNC; 10-16-2009 at 05:13 PM.
Reason: hit submit by accident
Using the Y angle for the spot color will definitely cause a moiré. If you use a C, M, or K angle you will have no moiré. The dots will in essence print directly on top of the process dot, which will NEVER NEVER cause a moiré. A moiré happens when the angles the dots are on are different, unless they are 30º away so they can land between each other. Try it, Luc; you can see it in film negs even.
Peace!!
_mjnc
MJNC is correct (sorry Luc).
In standard screen angle sets yellow is only 15 degrees away from C or M. As a result moiré is always there but it is usually not visible because the yellow is so pale. It can become visible if the yellow becomes contaminated - i.e. if it is darker. PMS 144 is a very dark yellow/orange color hence putting it on the yellow angle will create a visible moiré.
BTW the majority of screen sets run the yellow at about 108% of the frequency of the other process colors in order to further minimize moiré - without overly increasing dot gain.
As was mentioned in one of the posts, you could also try running the 5th color using a second order FM screen. If you're using a 175 lpi AM/XM screen then the FM should be about 35 micron otherwise if it's any finer you'll need to create dot gain compensation curves for the FM. Because 35 micron is a fairly coarse screen and because PMS 144 is a fairly dark color you may find that the screen is too visible making this solution problematic.
Running dot on dot screening, in this case, could be a problem not because of moiré as MJNC notes, but because dot on dot printing can cause significant color shifts with slight misregistration through the press run.
Gordo,
Did you mean 25 micron fm ? Would'nt 35 micron be too coarse if the AM is 175 l/in ?
Regards
BharatK
I'm speculating here because every shop condition is different.
25 will probably be too fine for two reasons - first the dot gain compared with 175 lpi might make the 60% tone too dark unless a tone curve is used to compensate (which would be guessed at unless a press test is done). Secondly, spot colors are not formulated to be halftone screened. As a result the pigment grind can cause poor ink transfer, mottling, and other issues. (sometimes it works though)
Here is a pic to show you what I mean. On the left is the FM screen on plate and on the right is the presswork using a PMS orange:
You can see how poor the PMS screened. When process yellow is FM screened (and the other three colors left AM/XM) you don't see this problem because process yellow is formulated to be screened. Also, because it's so light it's very hard to see if there is a tone reproduction problem. But PMS 144 is quite dark so any problems will probably show up clearly.
By going with the coarser 35 micron means that plate can run linear and the bigger dots make it easier for the ink. But 35 may be coarse enough, as you noted, that you see the dots.
For the fun of it, the attachment illustrates the situation (PMS 144 gradient over CMYK). Left shows PMS144 in the yellow angle, right shows it on the magenta angle. Make your pick... take a special look on the white area of the house, which one looks more like PMS 144?
Last edited by Luc St-Pierre; 10-19-2009 at 05:17 PM.
Reason: wasi ncomplete
For the fun of it, the attachment illustrates the situation (PMS 144 gradient over CMYK). Left shows PMS144 in the yellow angle, right shows it on the magenta angle. Make your pick... take a special look on the white area of the house, which one looks more like PMS 144?
I think something's wrong with your document. If I look at the separations in Acrobat - something is wrong with the screening. For example, here's looking at just the K plate:
How can the single K plate have a rosette?
The other single channels also look messed up - or am I viewing the document incorrectly?
The images placed in the PDF were already riped on a flexproof rip, they are a screenshot of my preview program. The color setting within the PDF is nowhere related to the images shown. If the angles seem unusual to you, it's because they are our regular flexo angles. The mathematics within the angle set is correct. so, what is your pick, left or right?
Thanks for all your help, guys. I think our options are to start with the spot screen at the same angle as the yellow, and if that looks bad, we'll run up another plate at 30° and see how it looks. It would be nice if Rampage had the ability to show me a screened composite, but no such luck.
Again, thanks for all your help. I'll let you know how it comes out.
Thanks for all your help, guys. I think our options are to start with the spot screen at the same angle as the yellow, and if that looks bad, we'll run up another plate at 30° and see how it looks. It would be nice if Rampage had the ability to show me a screened composite, but no such luck.
Again, thanks for all your help. I'll let you know how it comes out.
-- Rick
It's good to have made a decision, and it might work depending on the screening under the PMS.
I've attached a PDF of some patches of flat screened colors. (RGB screen capture from original 5/C)
The left set of patches is CMYK.
The center patches are CMYK plus an overprint of PMS 144 screened back to 60% using the Y angle.
The rightside patches are CMYK plus an overprint of PMS 144 screened back to 60% using the magenta angle.
View the PDF in PShop at 100% (to avoid moiré with your display's screen).
You may need to step back from your display to see the screen angle moiré clearer.
Compare the patches of color esp the oranges and blues. I think that you'll see that the center color patches display more moiré with the PMS using the Y angle than the M angle.
Again, you may get away with using the Y angle depending on the screening and image content below the PMS.
Here is a link to a screening guide, it may give you some ideas but I think it has been well covered here. The link is to the right under Expert Guide under Screening:
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Originally Posted by MJNC
