The Truth About Conductivity

by Jim Meagher

One of our customers was recently told that he couldn’t print without toning and drying problems because the fountain solution he’s using “doesn’t have the right conductivity.”

The last I checked, conductivity was not some abstract, ethereal force that makes presses print better…it’s simply a means to measure the concentration of a highly buffered fountain solution that can’t be accurately gauged by pH. That includes all modern fountain solutions developed within the last decade, or since the advent of alkaline papers. Therefore, if a fountain solution “doesn’t have the right conductivity,” how is this being judged?

The broad statement that “These plates always run best with a conductivity of 1,400 micromhos,” is pure bunk! It’s not likely that any two fountain solutions will read the same conductivity at the same concentration. In other words, a gallon of water with two ounces of brand X may read 1,800 over the tap water, while the same two ounces of brand Y may only read 900. It doesn’t mean that one is stronger than the other…they just read differently.

Select the Best

When called upon to aid a customer in his fountain solution needs, we always evaluate the entire situation in the shop.

What kind of plates are in use on each press? How good are the rollers? How many different presses are in the shop, and what dampening systems are in use? How good of an ink is in use?

Based on our experiences, we attempt to select the best product that may run on all presses in the shop. Sometimes this is not possible. Certain fountain solutions are wetter than others; some plates and dampening systems need such a product, while others need a dry solution with excellent plate cleaning abilities. Bargain priced, weak, or extremely low tack inks present their own challenges because of the extremely heavy ink films required to attain densities.

As an example, let’s take a Heidelberg MO with conventional dampening. We know that almost any fountain solution will perform well on such a machine, but if the plates they’re running tend to be sensitive, we’ll pick a specific product known to fight off tinting. We also know that this fountain solution should be mixed at the rate of  between 2 to 6 ounces per gallon and since it’s a modern, highly buffered formula the pH is built in and will read about 4.0. We’ll start at 4 ounces per gallon and run some sheets. Maybe the reverses are filling in after several hundred sheets, so we’ll go to 4.5 ounces per gallon and run some more. If some of the rollers are old and hard we may have to go to 5 ounces per gallon and the press will print beautifully. Sharp, crisp dots and no breakdown of the ink; drying is good.

Now we’ll measure conductivity. Let’s say that it’s 1,800 micromhos total, or 1,600 over the water that measured 200. Every time you mix it, the reading should be the same amount over the water reading.

After running the press for a while, paper dirt and other contaminants will cause the conductivity to rise, either in the water tray or in the recirculating tank. At some point, usually after several days, the press will cease to print as well as it was printing. Read the conductivity. Let’s say it’s 4,000. Stop and drain and refill the fountain solution. Then the next time it gets to, say, 3,800, stop and change the solution then, instead of waiting for trouble. It’s just that simple! 

It’s not a definite, it’s just a tool!

Another thing to bear in mind is the fact that today’s complex fountain solutions may contain from 10 to 20 ingredients that may each evaporate at a different rate, so it is highly recommended to begin each week with fresh fountain solution, although 3 days is the preferred time span.

As far as the pH goes, don’t mess with it. The manufacturer built it in, and if it reads 4.0, that’s what they intended it to do, and if you’re having ink drying problems, please look elsewhere!