G7 problem

[Salo]

Hello,

I tried to calibrate my SM52 using G7 methodology. The problem is achieving 0.54 D for HC. At 0.46 the primaries are oversaturated ( scumming to ). Seems that 0.33 it's the right density - but to low in regard to G7 specifications.
And another strange problem: the plates are made with CTP - polymer plates ( Fuji ). Every 5000-1000 sheets I must change the plates because I'm loosing the highlights ! - and this is more visible on the magenta plate. I verified the plates at the beginning- with an iCPlate ( the plates are linearized ) and the rasters are there ; but disappears when printing. Any ideas ?

Thanks

 

[Salo]

Sorry, 0.54 for HR ( by mistake is HC in my question )

 

[tmiller_iluvprinting]

Hello,

I verified the plates at the beginning- with an iCPlate ( the plates are linearized )

Thanks

Is this the calibration run? If so, why are you targeting HR density? You should be targeting solid and solid overprint Lab values. HR density and gray balance normally become the targets of the verification run after plate curves have been adjusted per the calibration run data obtained from the P2P target.

Best regards,
Todd

 

[Salo]

No, it's not the calibration - is the second run ( after adjusting plate curves ). This is strange. Could be related to the fact that the paper it's not ISO conforming ( a1 b-6 ) and the inks are a little outside standard ?

Thanks

 

[TerryWyse]

I was thinking exactly what Todd was thinking...sounds like you're trying to hit the HR value with linear plates which may/may not work.

Did you do the calibration ("linear") run and the verification ("curved") run on the same day with the same press crew? Doing it on different days with a different crew is almost always asking for trouble.

Can't help but recommend that you consider getting a G7 Certified Expert in there to help you out, especially if you're considering submitting this for G7 Master Qualification. Could save you a lot of time, paper and pain.



Regards,
Terry

 

[TerryWyse]

No, it's not the calibration - is the second run ( after adjusting plate curves ). This is strange. Could be related to the fact that the paper it's not ISO conforming ( a1 b-6 ) and the inks are a little outside standard ?

Hitting the paper and ink colorimetry shouldn't make any difference from a "G7" standpoint, it would only matter if you're attempting to hit a *specification* like GRACoL or SWOP 3/5.

As long as you are CONSISTENT in targeting the ink solids on the 2nd/verification run, the HC, HR and SC should all fall more-or-less in line with each other. On the other hand, if you've changed the *conditions* between the 1st and 2nd runs, all bets are off.

As far as your paper, those values you gave, a*+1 b*-6, sound like UNcoated offset values. If that's the case, the ink solids AND the HR value will not fall in line with "normal" G7 specs. The HR value floats somewhat in relation to the CMY Dmax value. It's usually a fairly subtle shift but the HR value won't necessarily be .54 (paper excluded) if you're calibrating on a low-density stock like uncoated offset. If you're using the IDEAlliance Curve software, it will tell you what the adjusted HR value should be for the CMY Dmax of the 1st press run.

Regards,
Terry

 

[Salo]

Thank you Terry. Yes, you are right. The calibration was in one day and the verification in the next day.I adjusted the SID's for Dmax ( "G7 extreme"). About consistency : it's a problem to hit exactly the same targets because the SM52 it's a little old and not 100% stable. The paper is not uncoated : is related as "coated matt " but probably with a lot of OBA. I'm using Idealink Curve 1.1 and the adjusted HR is 0.54/0.49 (K) The only thing that I changed in Idealink was the gray aim point from paper white ( a1 b-6 ) to a1 b-3. I was afraid for too much yellow after applying corrections. A G7 consultant it's impossible to find in my area in Europe - so I must do it alone

Regards,

Salo R

 

[TerryWyse]

The calibration was in one day and the verification in the next day.I adjusted the SID's for Dmax ( "G7 extreme"). About consistency : it's a problem to hit exactly the same targets because the SM52 it's a little old and not 100% stable. The paper is not uncoated : is related as "coated matt " but probably with a lot of OBA. I'm using Idealink Curve 1.1 and the adjusted HR is 0.54/0.49 (K) The only thing that I changed in Idealink was the gray aim point from paper white ( a1 b-6 ) to a1 b-3. I was afraid for too much yellow after applying corrections.

How did you arrive at the "Dmax" SIDs for your ink? Did you use max print contrast to determine target SIDs or some other method? The inks you're using, were they designed to use higher than normal SIDs (could be why they're scumming)?

Just my opinion, but I'm not sure using the "G7 Extreme" method and going for higher than normal SIDs would be advisable on an older press that admittedly is not 100% stable. You could be putting the press+inks "on the edge" of it's safe operating window and compromising stability.

As far as paper, that sounds like you've got a rather extreme amount of optical brighteners for a matte coated paper. Rather than modifying the paper white value for gray balance in IDEALink Curve, I think a better approach would be to measure the P2P targets with a UV-cut filtered instrument, that way you're getting the "real" paper value but without the OBAs.

I can't help but think there's something wrong with your technique that we're not getting to the bottom of. That, and I think you should abandon the notion of using G7 Extreme unless your inks are formulated for this.

Regards,
Terry

 

[Salo]

Yes, I verified the print contrast: K 46 M40 C 40 Y 34. The inks are "normal". I will try to repeat with lower SID values. About OBA- I don't have a UV cut device. Only I1 and X-Rite 530 without filtration. For the profile target I want to compensate via software. The G7 method for non standard paper white is applicable in your opinion ?

Thanks again

 

[TerryWyse]

The G7 *method* does not really specify a particular paper....it's only when you start targeting a *specification* such as GRACoL/SWOP3/SWOP5 that paper specs enter into the picture.

Many folks are confused about the G7 method as it relates to printing specifications:

The G7 method is only about a particular tone density curve and gray balance, all embodied in the "NPD" curve. Specifically, the gray balance is *relative* to the paper color, not absolute. In simplest terms, the midtone ("HR") gray balance a*/b* "color cast" should be roughly half of the paper a*/b*. That applies regardless of whether your paper contains OBAs or not. I only mentioned using a UVcut instrument because *I* find that I get a slightly better visual result.

If you combine the G7 method with a particular specification such as GRACoL Coated1, then things like paper L*a*b* and ink primary/secondary colorimetry come into play. But since you stated you're going the "G7 Extreme" route, you're by definition NOT targeting a specification so you're free to do whatever you want.

Terry

 

[gordo]

To Salo - What SIDs were you hitting for your G7 "Extreme"?

You could also try this method, which is pretty straightforward:

Quality In Print: DMaxx

best, gordon p

 

[Salo]

Hello Gordo,
the densities are: C1.65, M1.65, Y1.23 K1.95 - paper excluded
Regards,
Salo

 

[Ozkan Hangisi]

[And another strange problem: the plates are made with CTP - polymer plates ( Fuji ). Every 5000-1000 sheets I must change the plates because I'm loosing the highlights ! - and this is more visible on the magenta plate. I verified the plates at the beginning- with an iCPlate ( the plates are linearized ) and the rasters are there ; but disappears when printing. Any ideas ?

Hello

I had similar problem with Photopolymer plates as well. Some points which you really need to check :

- Use a temperature strip underneath of plate to define real preheat temperature. It should be measured between 100 - 125 C
- Be sure chemical is fresh, check processor parameters acording to Fuji (speed,temp,brush speed etc.) and readjust brush pressure
- Use gum which suggested by Fuji
- Recheck focus and exposure power. What I know exposure power is around 50 - 70 mj/cm2 for Fuji
- Some fountain solutions can be aggressive on plate surface. Ask your plate provider

If everything is done properly, then plate emission itself has problem. Call service.

Hope it helps

Regards
Ozkan