CMYK Blues

[bdenitto]

I agree with Dimitri, this seems to be a QA issue. If the color is correct on the front, & the proofs were showing the same color font & back, you should be able to expect a reasonable match be tween the front and back. The only possible for variation might be the finish on the sheet, (i.e one side dull the other coated) Do you have a snap shot of the entire run? Maybe you have some bad sheets.
Also 100m / 100c will produce purple. the chage from "blue" to "purple" usually take place after 80% M with the C being solid, just my 2 cents.

 

[Ravesh]

Hi There

I've just been through these woes and from experimenting and approval from my customers, to get a clean CMYK blue, the combination is C=100, M=65, Y=0, K=0.

Try it and tell me if it works, cos it works for me. In fact I've adapted this info for my clients who convert RGB blues from digital photography into CMYK images. They are happy.

Anyway, I hope this info helps

 

[Lukas Engqvist]

If your density to colourmetric corelation has been done correctly then the trap for blue should NOT have a magenta bias. There a many software packages out there that allow printers to adjust their 100 year old "in house densities" to acurately give the right colourmetric values compared to various international or other printing standards. Density only measures ink film thickness and not the colour or hue of the dried product. These software packages then allow for accurate TVI curves to give correct dot gain values to these standards as well - then hey presto the press is printing exactly as the proof just running to the new target desities and let the plate curve do the rest.

Simon this is a yes and no, TVI has nothing to do with 100% of C and M, so any software to control TVI curves will not help here. Trapping value does differ, but depends on so much. There is a also a reddening effect that can occur on certain papers. Also since the whole post concerns a purple or magenta biased blue, we don't know exactly what colour we are talking about. We know nothing of the viewing conditions... 100C100M is very sensitive to viewing light. Very seldom is it a colur that is consistent between screen and print. There is a theoretical "yes it can be printed" but on the defence of the printer there is not one of us that has never had a problem with that mix.
We don't even know if it is a digital or offsett etc , and on what paper any given CMYK value is very different depending on paper.

 

[Rick@IPCO]

I'm assuming, because of the quantity, that this was printed on an offset, rather than a digital, press. Regardless of the color; if the CMYK values are the same on the front and back, and the proof shows that they are the same, they should match on the final printed piece. This is just a bad print job.

 

[VLFPrepressMN]

Please remember that the stock has a smooth side and a wire side that can throw color, especially overprints. This, of course, would be invalid if the printer ran the form as a work and turn or tumble. If you have a spectrophotometer, the L*a*b* should be very close to L* 24, a* 17 b* -46. If you can measure, can you please post readings from the front and back? Simply put, the printer HAS to guarantee color from the front to the back. If they are not, find a new printer. This printer will not be in business long with these type of results.

 

[prepresscolor]

My best guess is your job was "ganged" with other jobs and the ink control was set up to print a great colorbar not a great product.
Try another printer next time and get "the exact match to proof" written into ur contract. Then be very careful what proof you authorize.
Good luck!