Another idea may be available to you. Open the underlying image in PSD. Mode change to LAB. Change color settings to heavy GCR or even Maximum GCR (custom settings) and mode change back to cmyk. Save as "name_GCR". Swap into job build. If this voids (or nearly voids) one of the separations, use that plate color's angle for the spot color.
[QUOTE=gordo;123465]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)
Gordo, a slightly related subject, we print all our book covers with a pms background that is a vignette which starts fading from 100% about 1/2 way up the page and goes to about 50% at the top of the cover. We have experienced problems getting this vignette to print smooth and I'm thinking could it be because we switched from 150 screen to 175 nearly 2 years ago now. We print one series with a dark purple pms #5255 and that ink is always wearing out the front edge of our plates on longer runs, we run other pms inks without this problem but they are usually shorter runs. Someone had suggested we have that color ground finer similar to what you've just described, is that a possibility you think?
Do you think we could go back to 150 for the pms vignette only and get by with it? We do have a small 1/4" wide band at 15% of this pms that crosses over the scenery photos on our front covers which we've always just run at the same angle as black at 45. See attachment...Any suggestions?
You're probably fine using the K angle for the PMS because there's very little, if any, K in your separation where the K overprints. Also K is 30 degrees away from M and C so there's no issue there.
Yes you can ask your ink vendor to provide you with a PMS that uses a finer pigment grind - one that is suitable for being halftone screened. This pigment grind issue is one that typically comes up when printers are using "extended process colors" to build screen tint combinations to replace spot colors - mostly used in packaging applications. Once the ink vendor knows that you are going to be screening the ink and once they know the dot size range (either in microns or lpi) that you are working with they can formulate the inks accordingly.
Sometimes the vendor will get it right on the first try, but sometimes it might take a couple of trials.
Going from 175 lpi to 150 lpi increases the size of the dots that the pigment need to stick to which makes it easier for coarser grind inks to work. The smaller the dot the finer the grind will need to be. So yes, going back to 150 lpi in your case will make things easier.
We ended up running the spot screen at the same angle as the yellow, and it worked out fine. You can see a tiny bit of a moire in some areas of the screen, but not a lot.
Thanks again for all the advice! Not only makes for interesting reading, but it really saved our bacon this time around!
LinkBack URL
About LinkBacks
Reply With Quote
