Dear Anne Dameria,
Regarding the issues you are encountering, it appears that what you perceive as a problem is, in fact, an inherent part of the printing process. A significant color value shift occurs post-ink drying, though tones generally remain consistent. For CMYK, any color shift typically manifests within 10 minutes; therefore, I recommend measuring sheets after this interval. To provide more precise recommendations, could you please specify which factors are currently out of tolerance? I have observed that black can lighten by 5-10% after 10 minutes. In such cases, I typically increase the black by 10% and re-measure after 10 minutes.
If a dry-back option is available, I suggest utilizing it. Please note that I am not referring to M3 mode, which I have not used for G7; I consistently use M1. I am open to any advice on this matter, as I have not personally used the dry-back option, nor have I seen it in Chromix curves, though it is present in Presssign.
Should you require G7 post-finishing, I recommend measuring the sheets after varnishing. I have not attempted this with drip-off due to concerns about measurement accuracy related to height. I generally conduct G7 post-varnishing, as varnishing is a mandatory step in packaging.
For proof setup, if you are printing TC1617 or similar charts to create an ICC profile, I recommend building the profile with varnish and using it for simulation. If gloss is the only difference, consider proofing on photo glossy paper for UV coating jobs to achieve the desired sheen. We typically proof on semi-matte or satin paper. Establishing two profiles-one with varnish and one without-would be beneficial. Could you please confirm if the CMYK colors are shifting post-UV varnish? Generally, only the gloss increases, with color shifts usually only visible in special color inks such as Reflex Blue or Rhodamines. Amount of shift varies to each ink manufacturer so this cannot be simulated in Proof.
To answer your second question - How to resolve - take drawdown print of the inks check dE. record the data ( immediate and after 10 minutes). I can explain why. In offset which used closedloop or open loop color control system the sheet is scanned as soon as it comes outside and correction data is sent to press in seconds. In such case the color shift after drying is not considered. If we know which colors shift post drying the target ink densities can be set according to this behaviour or switch ON dry back option is spectro system.
Apply varnish in half the print and check dE. If the dE is more than .5 compared to unsealed shade then expect color shift. This values should be recorded in the ink drawdown report and mark this in the ink can with a label so the operator understand which Ink can has color shift issues so he can check with ink chemist or QC person before starting the print run. This process is called Ink testing & approval procedure.
Regarding your second question on how to resolve color discrepancies, please follow this procedure:
1. Take Drawdown Print of Inks: Check the dE (color difference) immediately and again after 10 minutes, and record this data.
2. Understand Offset Control Systems: In offset printing that uses closed-loop or open-loop color control, the sheet is scanned immediately, and corrections are sent to the press within seconds. In these systems, the color shift that occurs after drying is often not considered.
3. Adjusting for Color Shift: If we know which colors shift post-drying, the target ink densities can be set based on this behavior, or the "dry back" option can be activated in the spectro system.
4. Varnish Check: Apply varnish to half of the print and check the dE. If the dE is greater than 0.5 compared to the unsealed shade, then expect a significant color shift.
5. Recording and Marking: These values should be recorded in the ink drawdown report. Please mark the ink can with a label indicating that the ink has color shift issues. This will inform the operator to check with the ink chemist or QC person before starting the print run.
This entire process constitutes the Ink Testing & Approval Procedure. I hope my answer met your query.
Best regards,
Panthala Selvan
With Regards
K.Panthala Selvan I Managing Director
PRESSMAN // IDEALLIANCE SOUTH ASIA
G7 Expert Trainer - South Asia
- PRESSMAN SOLUTIONS I IDEALLIANCE SOUTH ASIA
- PRESSMAN CENTER FOR PRINT EXCELLENCE
- PRESSMAN ACADEMY FOR PRINT EDUCATION & RESEARCH
No.2, Madha Koil Street I Nagalkeni I TN Malai road
Chromepet I Chennai - 600 044 I Tamil Nadu I India
----------------------------------------------------------------------------------------------------