Articles by CBAssociates

Published, Newspapers and Technology, May 2001

Let's stop chasing our (densities) tail!

I once worked with an old guy who was fond of saying, "what goes around comes around." I am sure I never heard him relate this to setting ink or to maintaining densities, but if he had, he would have been right.

I was reminded of this expression while conducting a print test a few months ago. The test was pretty straightforward and involved setting solid bars of cyan, magenta, yellow and black to industry standards. The operators did not have the benefit of an ink-preset system, so they started from their own estimated presets.

During the test I became involved with something that took me away from the two operators adjusting the ink. When I returned I noticed they had decided that one person would read the densities and tell the other the increase or decrease amount needed. After the adjustments were made, they grabbed a paper and started over.

My immediate reaction was that for these guys to be able to reach such an agreement they must work well together. However, my attitude changed after a while when one of them was working up a sweat running back and forth. What really got my attention was that they were making no progress toward adjusting the densities, and in some cases the densities were becoming worse.

A Fundamental Mistake

What was happening? They had made a fundamental mistake, and one that many operators make when setting ink. They believed the press would maintain a density level once it was set. This is not reality.

The operators, if questioned, might have been able to explain that the densities would vary. However, they adjusted the ink as if the press would maintain the density. What made this experience even worse was that they were using a densitometer to try to hit aim point numbers. This really caused them to chase their tail, so to speak. This is why setting to a proof sheet is a good idea ... but we will save that for another article.

The graphic represents the natural cycle or sine wave of a press. As the press rotates and the various components rotate and oscillate, there is an inherent variation in the amount of ink and water that reaches the plate. This inherent variation causes changes in densities. A big difference between newspaper and commercial presses is that commercial presses are designed for less inherent density variation.

Of course, running collect causes more problems. Each side of the cylinder requires a different ink volume. This is particularly troublesome if the difference is significant.

The chart also describes the aim point of black ink density at 1.05 densities units (these are not percentages). The NAA and SNAP standards call for a variation not to exceed 0.05. Therefore, the upper control limit (UCL) should be 1.10 and the lower control limit (LCL) should be 1.00.

Before I receive any "fan" mail, let me point out that the standards are technically for the variation on a proof, but it is understood that they will apply to printing.

If the density readings all fall between the UCL and the LCL, the process is said to be within specification and control. Conversely, if these readings are outside the upper and lower boundaries, they would be out of specification.

The curved line represents inherent density increases and decreases over 25 consecutive copies. This number of copies, used in the example, is based on a real test and is typical of certain types of presses. The important thing to note is that the values increase and then decrease.

The folks in my test got into trouble because they happened to take some low readings when the press was in the increase density cycle. When they took the next measurement, instead of being on the aim point or too low, it was too high. Had they known that the press was in the increase cycle, they would not have added as much ink. Using the densitometer and trying to be precise caused them to chase the densities too much.

Another reason they were working up a sweat was that they could not set the water level low enough. This caused the inherent fluctuation to be even greater than the plus or minus 0.05 that could be expected from an average press.

So the harder they tried, the more frustrated they became. They were having as much luck getting the densities within the specification limits as they would have herding cats. We had to call off the test.

How do operators stop chasing the densities?

The first thing is to set the units to manufacturer's specification, this includes rollers and blankets.

Step two is to make sure all the colors and the fountain solution are compatible. This can be determined by running a test that includes standing heads, logos, color bars and solid one-inch bars of each color across the page. If the printed sheet is dry to the touch and there is a smooth solid lay down on all colors, they are working together well.

When the colors are printed to the proper density range, pull 100 copies. These will be posted in the color booth for the operator to use as a reference. These papers should be changed out on a regular basis.

The most important thing to do, which is what the champions do each and every run, is to run the water as low as possible. Who are the champions? Some of them are the winners in the IFRA color contest and of course, most USA Today sites.

When the press is right, when the chemicals are right, and when the water is low, you should feel a bit like the Maytag repairman as you set the ink, check it periodically, and reflect on the lack of anything to do during the run.

[HOME]