I have been so immersed in virtual proofing over the last several posts, that I had almost forgotten how much I still love the smell of ink in the morning. Last week I had the privilege of spending two days assisting a customer in the set-up of our software primarily for use as a pressroom monitoring tool.
The experience reminded me of #55: Just Measure It! The customer is a web offset shop and has the same problem that most of our digital printing customers have (Oh, I love the smell of toner in the morning too!). The problem is that their press product is finished product and has no trim. Color bars are not an option on production work, and changing the design to incorporate color swatches would also be impractical at this time.
The solution turned out to be the same solution we employee with our digital printing customers. A test form is put on press twice a day and the results of those measurements are used to verify conformance to density standards across the web. A second control strip can be scanned to gather other print metrics like TVI, Print Contrast, etc.
The results in a sister shop have been improved consistency from day to day and the ability to monitor changes in density and TVI from morning (cold press) to afternoon (warm press). In a perfect world I would love to see color bars on every job, but we thought outside the box and found them a solution that allowed us to measure. Once they started measuring quality and consistency improved. Profitability and productivity are never far behind quality and consistency improvements.
I raise the challenge again…today start measuring something in your color workflow that you are not measuring today. Within seven days those measurements will point the direction you need to go to improve the quality and consistency of that process.
Earlier this month I was visiting a customer who utilizes multiple ColorMetrix licenses to monitor and control; plate making; proofing; and pressroom. Several years ago this customer used ColorMetrix in his plate making operation to uncover a processor replenishment problem that not even the plate vendor was able to unravel. During this visit, he told me about a recent experience involving a pressman who came to him asking for a new plate so that he could achieve a match on press. For some reason he could not get the cyan to fall in appropriately. My customer consulted his ColorMetrix plate database and confirmed that the plate was properly made. He then measured a press sheet provided by the pressman and compared it to his historical data for that press and paper combination. The cyan dot gain (TVI) was about 10 points away from the expected values.
He agreed to make a new plate with an adjusted curve in the interest of getting the job off press with acceptable color, but also suggested the pressman take a long hard look at the cyan printing unit. Before the plate was even processed the pressman returned and said to never mind he had uncovered a roller problem in the cyan unit.
Yes, all the data collection our client does takes time and effort, but what is an hour of your press time worth? He pointed out that this is not an isolated occurrence. Just having a densitometer and measuring density and dot gain would have done no good in this situation. My customer and his pressman needed to know what the expected density and dot gain would be on the press and paper combination being run.
By simply measuring the OK sheet from most jobs, within 30 days you will have a very substantial database to fall back on when problems like the one illustrated above occur. So, process control is not free, but instead an investment with a fairly easy to calculate return. There are more examples of how process control has saved our clients money at here at JimRaffel.com, so feel free to read the archives.
This week I will be providing more information about the MacDermid Printing Solutions Stabil-X press trial April 17th and 18th . This week I will review the variation data from two of the trial conditions:
- STX opt – Stabil-X blanket run at optimum packing level
- Press std – The set-up of the press when we arrived
The TVI graph from last week showed the mean 50% dot gain for the STX opt. to be 24.817 and the Press std. to be 25.556. In addition to the lower overall dot gain with the Stabil-X, the standard deviation of the Stabil-X opt. was only .752 compared with 1.088.
The density of the two runs are very similar as well as the associated standard deviations: STX opt. 1.489 and .018; Press std. 1.522 and .016.
These two graphs plot each of the 10 samples measured for each trial condition. The graphs also show the mean as well as 3 standard deviation +/- control lines.
If you would like more information about the MacDermid Stabil-X blanket, please contact me and I will put you in touch with the right people at MacDermid.
On April 17th and 18th I had the pleasure of participating in a press trial with MacDermid Printing Solutions to evaluate the effectiveness of their new Stabil-X offset printing blanket. I am writing today about the TVI curve of the various trial conditions.
We ran five different conditions during the course of the trial. All the trials shown in the graph involved only one printing unit running magenta ink. The curves also represent the averaging of 10 press sheets. The five trial names and descriptions are:
- STX opt - Stabil-X blanket run at optimum packing level
- Press std - The set-up of the press when we arrived
- STX -.003 - Stabil-X purposely under packed by 3 thousandths
- STX +.002 - Stabil-X run at 2 thousandths over
- STX +.004 Stabil-X run at 4 thousandths over
As one might expect the STX -.003 has not only the lowest TVI, but also a very poorly formed curve. A pretty good example of why you do not want to run your press under packed.
The Press std curve shows how this shop runs the press on a regular basis. Notice the hump in the TVI curve from 25 to 50%. Not an uncommon condition on many presses.
The STX opt curve is much smoother than the Press std curve, missing the hump from 25 to 50%. Also, run at virtually the same densities the dot gain (50%) and overall TVI is lower at all points than the normal press set-up.
Even the two STX over pack conditions produced smoother overall TVI curves than the press standard set-up. While the TVI is higher in most cases this is to be expected when adding that much squeeze to a blanket that really does not need it.
I will continue to write about this press trial for a least 2-3 more weeks. There is a great deal of data and information to still go over. I even have some sheets here I will be doing additional readings on.
If you would like more information about the MacDermid Stabil-X blanket, please contact me and I will put you in touch with the right people at MacDermid.
Over the coming weeks I will be writing a great deal about my last two days in Chicago. Kevin Kocher of MacDermid Printing Solutions (offset blanket manufacturer) invited me to a press trial of their new Stabil-X blanket. So, right about now if I was one of my readers I would be thinking how exciting can an off-set blanket be? In a word this blanket is cool. It truly is the first revolutionary technology change in blankets in decades. In short this blanket is a patented combination of a polymer backing (instead of fabric) with Kevlar fibers running through it as well as synthetic fibers to replace the nitrile rubber and cotton.
We took a great deal of measurements during this trial, and while I have not had time to fully review the data I can tell you that this blanket printed better. Better being lower dot gain at the same density levels as conventional blankets, a smoother shaped TVI curve than traditional blankets, and most importantly less density and dot gain variation in sequential pulls.
Over the coming weeks I will be including both numeric and graphical results of this test, showing how we utilized ColorMetrix to confirm the visual results with objective factual data.
Part 5: I should start by saying I have covered the topic of using graphic arts densitometry to evaluate inkjet proofs once before. Back in July ’05 GN#5 addressed this same issue so you may wish to refer back to it. I considered changing this topic, because the title is a bit inflammatory. Understand that my frame of reference is users of our software who rely upon density and TVI as process control measurements for inkjet proof production.
Far too many times I have seen the density and TVI values stay within tolerance, and yet the Delta E shifts can be huge. Those of you who follow the blogging I do at JimRaffel.com (yes, I write more than once a week sometimes), saw a graph of the spectral response of the Red, Green, Blue, and Visual filters used in graphic arts densitometry. Those filter responses are specifically designed to address the spectral response of process cyan, magenta, yellow and black. While I was not able to find them for this week, I have seen graphs which compare the spectral response of offset printing inks with typical inkjet inks. By next week I will either find the curves or reproduce them myself once I am back in the office. A picture will be worth a thousand words when I post those graphs at JimRaffel.com.
Coming next… How important is Gloss?
Erik: Michael Litscher (Colormetrix CTO) provided this and said that a picture is worth a thousand words. I hope this helps in your understanding of the Visual filter.
Part 3: TVI in and of itself is not a bad thing: Back when TVI was called Dot Gain, I remember going into print shops and having pressman tell me “No, we don’t have any dot gain.” This was not ignorance (they knew they did), but instead a misconceived notion that TVI was a bad thing. I always countered this by saying that Dot Gain is not bad; however, NOT knowing what you Dot Gain is, is a bad thing. Think of it as trying to get from one city to another in a car without a map. We need to know where we are in order to get where we are going.
Coming next…Part 4. Density is king
Part 2: GRACoL 7 appears to be taking our pressrooms in a direction where TVI will be significantly less importance in monitoring production run stability. Instead GRACoL 7 is based on maintaining gray balance utilizing density and L*a*b* values. Over all, I feel this is the right direction to go and from what I have heard and seen several test press runs have proven this to date. Even GRACoL 7, however, recommends taking a look at CMYK TVI values when the system does not seem to be working as intended. TVI and TVI variation are still incredibly powerful and simple measures of press stability. I have watched real pressroom experts track down loose blankets and other press problems by first taking a look at TVI numbers, then looking for the actual mechanical problems. (NOTE: If you have not read the GRACoL 7 draft quite frankly you must. This methodology will become a barrier to entry very quickly.)
Coming next…Part 3: TVI is not a bad thing.
