SPOT COLOR CURVES

[E]

I have been working on getting our system color calibrated and the correct cutbacks for press dot gain, we have discussed if there should be a cut back on Spot colors as well as CMYK. I have run press screen tests, compared to screens on plates and found that the press sheets were of course running dark. I applied a curve in our Express Workflow, read the values on plates and again on press and I am fairly happy with the results so far (I might need to tinker with lower screens a bit). My problem is now we have to adjust our screen values in jobs that repeat to match previous run jobs before the curve was applied and I keep repeating myself as to why we need to do this. I first want to confirm that we should be doing this (curve on spots) and second how others handle spot curves or not. I need help to even convince my boss that this is correct much less the rest of prepress personnel.

Any input would be helpful. I don't mind if I am wrong in my thinking, I just want answers to stop all this frustration before I loose the rest of hair!

Thanks all.

E

 

[almaink]

Re: SPOT COLOR CURVES

I use the same curve for Pantone's that I use for black ink.

 

[Luc St-Pierre]

Re: SPOT COLOR CURVES

Pretty much the same for us. Black cutback is blindly applied to spot colors. Same for screen angles except, of course if 2 spot colors interact.

 

[gordo]

Re: SPOT COLOR CURVES

RE: "I use the same curve for Pantone's that I use for black ink."

From visiting many many shops - this is very standard practice.

If spot inks are regularly used for extended process color printing or spot color replacement, then in that case printers will usually create custom curves for the extended process colors.

best, gordo

 

[Paultheprinter]

Re: SPOT COLOR CURVES

After reading this thread i think curve compensation for spot colors is a difficult task to undertake, especially as the weight in which spot colors are run varies very much. This may be due to the strength of pigmentation of the individual spot colors itself, a 072/ reflex blue may be as high as 1.8 where as a orange may be 1.2. I appreciate that these results may be due to a densitometer reading colors with a less than accurate filters causing inaccurate density values and six filter densitometers may help, but absolute ink film thickness may be a better way to determine dot gain is a better way to go giving more consistent results, but as i see it this is not possible at the moment and therefore guessing ink film weights and dot gain is still a bit of guess work unless the same ink and substrate were use in previous cases to gain the characterization data and create curves. What do you think?

Paul

 

[Lukas Engqvist]

Re: SPOT COLOR CURVES

If you have spot jobs you can put a stip and see what dot gain you get. Decide what dotgain you want and get a curve from there. You need to document what you get and build classes so that you can decide what curve is fro shat spot on what paper… or just use the black curve,

There aren't hardly any good ways for the customer to proof tints of spots anyway ;P so you can tell them you get waht you get.

 

[E]

Thanks for the input to everyone. The main problem is matching jobs that were printed before we had the curve on spot colors. I had originally used the same black curve applied to our spots, but we were not getting good results, I then looked at our cyan curve which is a bit more linear and from our last press run we have found we are pretty damn close. We will be testing again hopefully this week to verify what we get.

Thanks again!

 

[E]

One more thought on this subject. When the standard process black curve is used for spots, are you talking about linear curves or bell curves? Just to be specific.

 

[rich apollo]

yeah, what Almaink said.