G7 lab values on Press

[indy jones]

Hello,

I have strange problem with our inks for our offset press. I can hit primaries and secondaries lab values to G7 with in 2 to 4 Delta E. The problem I have is the 4c blacks, 80c,65m,65y,100k. We are printing in blueish range when it should be in the magenta side to Gracol 7 profile. We use Idealink to achieve gray balance. Has anybody experience this problem with shadows blacks?

 

[Bret Hesler]

Hello,

I have strange problem with our inks for our offset press. I can hit primaries and secondaries lab values to G7 with in 2 to 4 Delta E. The problem I have is the 4c blacks, 80c,65m,65y,100k. We are printing in blueish range when it should be in the magenta side to Gracol 7 profile. We use Idealink to achieve gray balance. Has anybody experience this problem with shadows blacks?

80c,65m,65y,100k should be dead neutral by my calculations. I have seen blue shadows and it is usually because of a problem with the 100c,100m,100y. In Idealink, on Analyze Color tab, does the blue line in the CMY gray balance window dip down as it approaches 100? Also, the default settings in the gray options are to reduce the effect of the gray balance compensation above 50% Cyan. You can increase the number to get more of a gray adjustment, but I strongly advise against it if the 100c,100m,100y is not close to neutral.

To get a more neutral 100c,100m,100y can be tricky. First start with your CM and Y solids. Are you a bit heavy on the Cyan or weak with the Yellow, or both? If they are good, then you have to look at overprints. Can your red and green take a bit more yellow, or can your blue take a little more magenta? You might have to play with the tack and or strength of you inks to really dial these in.

Bret

 

[tmason]

Indy,

If you are G7 Master Printer, you should have samples of your press sheets and proofs from your original qualification runs. Compare your current press state to those. Has anything changed? Ink, blankets, paper, plate curves, fount.
Check your ink density, even though the Lab values are good. Make sure the Lab values are good at the correct density according to your original G7 calibration. Approximate values, C-1.45, M 1.45, Y-1.0, K-1.70. Be sure the trap sequence is KCMY. Check the dot gain on press to make sure it is printing properly. IS IT SLURRING?
Measure the plates and verify the dots on the plate match the output curve and the plate output from your qualification.

Does the color you have now, match the original qualification run? If it does and you do not like the results, you should profile to your press. You should generate your own profile to your press output and not use the Idealink profile. This is a generic profile developed from an average, not necessarily what your shop is producing.

good luck,

Todd

 

[tmason]

Indy,

I just re-read your issue. You are putting down way too much ink.

Try running, 100K, 40% CMY.

Todd

 

[Stochast]

Rich Black recipe

Rich Black recipe

Do try lower values, 40, 30, 30, 100. If you need more than that, of course use the actual mid-tone of 48.8, 40, 40...

 

[deggers]

G7 lab values on Press

May I ask, please, what is your print order?

The reason I ask is because we had a similar problem, except with yellow. Our print order is KCMY. The way we resolved it was by creating a press run to help us find the most neutral undercolor. The press run consisted of a series of patches with 100%K, 50%C, 40%M and varying amounts in 5% increments of Y from 0% to 40%. Then we took our XRite 530 and measured each patch several times, averaging the measurements for a patch together and picked the most neutral undcolor combination. Whereas neutral gray is defined by Idealiance as 50-40-40 CMY and seems like it should be the ideal choice for rich black undercolor, we found that with our print order the best combination is 50-40-25.

We also Included on this press run a max ink finder. This is a simple file that puts ink down in growing amounts. Its purpose is to find where you stop benefiting by adding more ink. The amount of ink you are applying to the paper seems really high. Ink is not cheap. You might consider creating a run that helps you find that value, then consider rebuilding your profiles to create GCR numbers under the max.

 

[Greg Imhoff]

Indy's shadow gray balance question

Indy's shadow gray balance question

Hi Indy: Can you specify what types of paper, ink and Ph conditions ur running to?

Also I may be misreading the cmy/k need results yet believe G7 shadow tone targets for gray balance is not 80c, 65m, 65y. Try plating and running to 75c, 66m, 66y and your blue cast may then level out.

Sincerely,
Greg Imhoff
(708) 557 -2021

Hello,

I have strange problem with our inks for our offset press. I can hit primaries and secondaries lab values to G7 with in 2 to 4 Delta E. The problem I have is the 4c blacks, 80c,65m,65y,100k. We are printing in blueish range when it should be in the magenta side to Gracol 7 profile. We use Idealink to achieve gray balance. Has anybody experience this problem with shadows blacks?

 

[User Name]

Hello Indy:

There are only two ways to produce complex color, or for that matter neutral gray balance patches on a printing press using four color process.

The first way is to have balanced halftone screen builds up to about 60% of scale. After that trapping (over printing) is the most important to control.

The screen builds can be managed or assisted by pre press; but the trapping is in the pressman's and ink supplier's hands. Trap values dictate the colors you will reproduce, whether it is a two color trap or a four color overprint. Trap is effected by ink film thickness, laydown sequence, blanket packing, pressure, ink / water balance, tack and viscosity of inks. (There are other influencing factors, but these are the most obvious.) All or most of these can and should be measured, especially when a G7 certification form is being run, otherwise things can change and you will lose your gray balance control.

Of course you can influence the 3/4 tone neutrality by implementing GCR / UCR, but then this starts to move you away from GraCol towards a more traditional approach.

Retroman