G7 & ink sequence

[tnflyer]

Attempting a G7 calibration on a press and having trouble with the overprint colors, (red, green, blue). Ink supplier suggests changing sequence to KCYM. I am skeptical. Thoughts? I would really like to hear if anyone has tried this & your experiences. Has anyone profiled with varying sequences?

[color_matters]

I have come across this blog by Gordon Pritchard hope it helps.

The Print Guide: Ink Sequence

[rich apollo]

Attempting a G7 calibration on a press and having trouble with the overprint colors, (red, green, blue). Ink supplier suggests changing sequence to KCYM. I am skeptical. Thoughts? I would really like to hear if anyone has tried this & your experiences. Has anyone profiled with varying sequences?

G7 is intended to run a KCMY ink sequence. I don't suppose there's any colorimetric reason you couldn't run the inks in another sequence, but I really don't think it's a good idea. You'll be increasing the risk of backtrap from M to Y, and you will distort your ink trapping.

What is the specific problem you're having?

[tnflyer]

G7 is intended to run a KCMY ink sequence. I don't suppose there's any colorimetric reason you couldn't run the inks in another sequence, but I really don't think it's a good idea. You'll be increasing the risk of backtrap from M to Y, and you will distort your ink trapping.

What is the specific problem you're having?

The problem seems to be magenta. I can get CYK to less than 1 Delta E. Magenta is always borderline. I can get blue & green overprints to 2 to 3 Delta E Adjusting densities sometimes brings red overprint close to tolerance, but still out, and gray overprint always out. Ink supplier says magenta & red will fall in if I change sequence to KCYM. My concern goes beyond solid ink LAB. What will happen to overall press gamut with a change in sequence? I could profile the press with different sequences, it might even be fun, however I would probably not have that much press time available (big surprise).

[gordo]

Along with the comments by Rich - a KCYM ink sequence will skew your color gamut and mean that you will have difficulty printing to an ISO/GRACoL 7 proof. Your greens will suffer, your blue/purples will be better, your reds will skew towards orange especially since yellow is usually the greatest area coverage in separations.

You need to talk to a different ink supplier.

best, gordo

[tmiller_iluvprinting]

You can measure a draw down of the magenta ink to see if it indeed is an ISO-12647 compliant ink. I f you can't find an ink film thickness from the draw down that gives you passing Lab numbers, then it won't matter what ink sequence you use. It is possible that your ink could fail right out of the can..
Regards,
Todd

[Bondi_dan]

Along with the comments by Rich - a KCYM ink sequence will skew your color gamut and mean that you will have difficulty printing to an ISO/GRACoL 7 proof. Your greens will suffer, your blue/purples will be better, your reds will skew towards orange especially since yellow is usually the greatest area coverage in separations.

best, gordo

ISO Standard 12647-2 Series specifies KCMY sequence. The G7 Methodology is in sync with 12647-2 and also recommends KCMY.

Regards,

[gordo]

@tnflyer

What solid densities are you running? (also status T or E?)
What are your overprint RGB trap values?
Which instrument are you using to measure the CIE L*a*b* values?
What formula are you using to calculate DeltaE?

best, gordo

[tnflyer]

@tnflyer

What solid densities are you running? (also status T or E?)
What are your overprint RGB trap values?
Which instrument are you using to measure the CIE L*a*b* values?
What formula are you using to calculate DeltaE?

best, gordo

Gordo,
lowest Delta E (76) values are at;
C-1.37
M-1.45
Y-1.02
K-1.58 status T
Using both X rite 530 & i1pro, there is a bit of difference in readings in the 2 instruments, but they are close. Using 530 at press & i1 with measure tool for the curve software.
I get that the ink supplier is trying to get me off their back, however, they don't seem to get that there is a concern beyond solid ink LAB, it does me no good to hit solid ink LAB numbers & then shift gamut. I'm mostly wondering how accurately can a shift be predicted (if at all) without actually re-arranging the sequence?

[gordo]

Gordo,
lowest Delta E (76) values are at;
C-1.37
M-1.45
Y-1.02
K-1.58 status T

I get that the ink supplier is trying to get me off their back, however, they don't seem to get that there is a concern beyond solid ink LAB, it does me no good to hit solid ink LAB numbers & then shift gamut. I'm mostly wondering how accurately can a shift be predicted (if at all) without actually re-arranging the sequence?

Your SIDs are where they should be.
What are your trap numbers?
What are the CIE LAB values of your CMYK and RGB solids?
What is the LAB value of your paper?

Just trying to confirm where the failure is occurring.

best, gordo