process Density and Dot gain questions

[verbena]

Hi Guys

Im new at 4 colour litho process work. Ive got a calibrated densitometer. what density and dot gain values should i be looking at. also should i be zero-ing the paper on every pull for murray-davis or should i add the paper density to the equation. Also what print sequence should i be using. the last few jobs i did was ycmk, not sure that this is right.

please help.

 

[xallux]

Sequence depends on ink tack. I have always run KCMY, black being down first, and haven't had any problems. As for densities: K - 1.90, C - 1.30, M - 1.30, Y-.90. Now those are just starting points. Adjust as necessary for your inks, paper and press. Ink densities on offset paper will be higher than on gloss paper.

 

[verbena]

Thanks Xallux. I'll give that sequence a try. About the density measurements, do you zero the paper for the pull or does that measurements include paper.

 

[xallux]

I usually zero out for each job, just so my starting point is the same. Let me know how everything works out.

 

[PieterPrint]

Hi,

All the people i know use the same Density values. C=1.40 M=1.40 Y=1.30 K=1.80. These are the values i use when i'm printing glossy paper. If i'm printing uncoated paper the following values work fine. C=1.15 M=1.15 Y=1.00 K=1.50.
The values offcourse depend on sort of paper and photo quality. I also always calibrate my D meter before every job.

With love from Belgium

 

[RichardK]

The previous postings are all in the ballpark - ultimately you're selling the job not the control strip. ie if the job looks like the proof the densities are pretty much irrelevant.

However, print sequence, particularly on coated stock is crucial. KMCY is the way to go for the majority of work, especially if there are colour values that are close to reflex blue (80m/100c). You can switch to KCMY if you have colours values like (100m/50c). This improves the 'lift' or 'trap' between those inks.

You don't mention how many units your press has tho' - this can change the above advice regarding sequence considerably.

 

[PieterPrint]

colour sequence

You should indeed not only look at the colourstrip. That's what they teach you at school.
The colour sequence we use is KCMY on a 4-colour ryobi press. We also have an eight colour Roland 500. But we also use the KCMY colour sequence there. I sometimes change the sequence if it's a difficult job.

With love from Belgium.

 

[Stu]

With regards to zeroing the densitometer, always zero the paper as the different "whiteness" between different stocks will have an effect on the result.
Murray Davies is a conversion factor, also called an n factor or yule nielsen factor. Murray Davies is a factor of 1, meaning if you multiply a figure by it you will get the same result. and is used to calibrate a substrate, it is usually only used on plates, because of the number of different papers out there it would take too long to find the yule nielsen factor of all of them, which is why we use murray davies. This has little or no effect when measuring density and is only really needed with dot gain

 

[birdz]

ink density values will vary with the type of sheet your printing, do a calibration run with a GATF or Gracol test image and run your color to proof - then see where your densities are at. Ink density is nothing more than a guideline - yes its great to have proper density but if the press sheet doesnt match the proof the whole run is a bust.

 

[bluebeep]

ink density values will vary with the type of sheet your printing, do a calibration run with a GATF or Gracol test image and run your color to proof - then see where your densities are at. Ink density is nothing more than a guideline - yes its great to have proper density but if the press sheet doesnt match the proof the whole run is a bust.

Zeroing densitometer once should be ok remember its all about reflection
drying will give a lower value more on uncoated stock due to absorbtion

 

[4 color GTO]

The previous postings are all in the ballpark - ultimately you're selling the job not the control strip. ie if the job looks like the proof the densities are pretty much irrelevant.

However, print sequence, particularly on coated stock is crucial. KMCY is the way to go for the majority of work, especially if there are colour values that are close to reflex blue (80m/100c). You can switch to KCMY if you have colours values like (100m/50c). This improves the 'lift' or 'trap' between those inks.

You don't mention how many units your press has tho' - this can change the above advice regarding sequence considerably.

Exactly!! My densitometer is only used when I can't match my proof and have to figured out who screwed up what. LOL

 

[lildaddy50]

Always run your sequence K,C,M,Y It is possible to run the yellow down first ,but only if you order "1st down yellow" from your ink supplier. You can check the process densities by measuring the density of your pms book. Look in the front of the book and you will see the process colors. Measure them with your densitometer and write it down. Now you may want to add 5 points to each color to compensate for the dry back issue. When your printing and measuring densities,the ink is wet. In the book the ink is dry.

I have been doing this for 30 years. The standard density for process is, K-170-200 cyan-130-140 Magenta-140-150 yellow 95-110 when your running a black solid you can run the den. at 200. If there are lots of screens run at 170. It depends on the job.

Make sure when you take the measurements from the pms book that you read "cyan" not process blue! Process blue is much darker than cyan.

Rod

 

[pressman57]

The previous postings are all in the ballpark - ultimately you're selling the job not the control strip. ie if the job looks like the proof the densities are pretty much irrelevant.

However, print sequence, particularly on coated stock is crucial. KMCY is the way to go for the majority of work, especially if there are colour values that are close to reflex blue (80m/100c). You can switch to KCMY if you have colours values like (100m/50c). This improves the 'lift' or 'trap' between those inks.

You don't mention how many units your press has tho' - this can change the above advice regarding sequence considerably.

I've been having some problems running dark blue screens in process jobs using KCMY sequence. When using KMCY do you have to reduce the Cyan or will it trap OK on its own? Thanks for the post. I never considered changing the sequence, but looking back I think it could be a trapping issue.

 

[gazman]

not sure if its too late to join in, but running KMCY is the way to go on dark blue screens. You shouldnt need to reduce the cyan as C and M tacks are pretty simular.
Cheers Gazman

 

[RichardK]

We've been running KMCY sequence for nigh on 20 years without trap issues.
But as you rightly say gazman, the tack values of C & M are very similar.
If you run into trapping problems then you could try a different ink set, or use a low tack version of the cyan.

 

[NotAGooner]

Have always ran KCMY unless there is a heavy black coverage with no opportunity to split the black onto two units, then we run a low tack black on the last unit

 

[turbotom1052]

try not to get too dependant on that densitometer. ive seen lots of pressman live and die by densitometer readings. while your reading all them color patches that huge honkin hickey is in half the job. to me a denistometer is a tool to verify what my eye is seeing. its also helpful when printing crossovers over multiple forms. exact match pms spot color is a good time to whip out the densitometer too. i once worked for a guy whos answer to saving money was to use minimum sheet size. we rarely had the luxury of color bars. being forced to rely on my eyes and my brain was perhaps the best learning experience for me when it came to running 4/c process!!!

 

[Dan1]

Watch getting too far off standard densities when matching a proof also. Densities way too low will not leave enough ink film on the rollers and you will fight color variation during the run. Too high and variation, plugging and ink stringing off the image ( this is especially evident with black type ) could all be potential problems along with having to increase the amount of fountain solution used to keep the plate clean possibly causing emulsification problems with the inks.

 

[lildaddy50]

Dan is right on several points. If your not running enough ink, your water will start to over take the ik and you will be up and down and unable to control a steady color. Also, a thinner film of ink will make your blanket more tacky and you will pull more paper particals off the sheet. (hickies) Thats why it is imprtant to stay in areasonable range when it comes to densities. Here are the standard densities for running 4/c process.

Black 170- 200
cyan 130-140
magenta 140-150
yellow 95-105If you are running a pms color ,then take a reading with your densitometer right off the pms book. This will give you an idea right off the bat of where you need to be whith your pms density. Usually you will have to compensate for the dry back factor that has occured on the draw down in your pms book. That mean that the book will read 3-5 points lower than the wet sheet that is coming off your press.

If your a new pressman, than Isuggestou use yor densotometer until you can recognize the density of you process colors with your eyes. This could take years. Even after 32 years as a pressman , I still use the desitometer to get me close to standard process densities on every job. It is a very useful tool inbetween make ready pulls to see if your initial reading of the plates was too much or not enough. Afterall , it is just an educated gues when one is setting his ink keys by looking at the image on the plate.

Rod (32 yrs exp.)

 

[Data]

I use a densitometer like register marks. Get the initial setup and then go by eye, thats if i use it at all.

I feel one can get so hung up on using these aids

Our values for a conventional screen are
C=145
K= 185
M=140
Y=100

For print order it depends on the job and work scheduling.