Print quality

Hi, I’m looking for some answers to my print quality issues.
I have restored an Eaglet treadle platen press (copy of a Golding pearl). The problem is that when printing, the impression looks even and ‘solid’ with almost no impression showing on the back on 100gsm writing paper, but print is not crisp. It looks messy, with the ink in tiny beads around all the edges. There is mixed type ranging from 60pt to 18pt.
I am using litho inks which work fine on my Adana. I trained as a letterpress printer many years ago so feel i should know how to cure this.
I am sure other have had the same problem and can help me with some solutions (probably already on the site somewhere)
Thanks

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The ink rollers have heavy pressure , need adjustment

If you were not experienced, I would say you have too much ink, and it is squeezing out beyond the printing surfaces during the impression.

Since you are experienced, it could be that your rollers are set too low, as justyas003 says above, and you are inking the upper part of the shoulders of the type, and then transferring some of that ink during the impression.

As already mentioned one possibility is too much ink and the excess is being squeezed out or the rollers are too low and ink is being left on the edge of the type or both.

Letterpress ink is not the same as litho ink, I was advised by a chemist who worked for an ink manufacturer many years ago to dilute the litho ink with a small amount of boiled linseed oil for letterpress work. I can see the difference when I use litho ink on a table top but never tried litho ink on the Heidelberg.

On a separate but related topic, most ink is thioxotropic, meaning it has “false body.” When it is freshly taken out of the can, it is relatively thick. When it is put on the press and worked up by the rollers, it becomes somewhat thinner. The reason this happens is that the pigment particles tend to “agglomerate” in storage, which means that they tend to stick together. When the ink is worked, the stuck together particles tend to break apart again, making the ink thinner. Some ink pigments agglomerate more than others. (An analogy would be yogurt: when you first buy it, it is like a solid jelly, but after it is worked up with a spoon, it is more creamy).

For this reason, it is not a good idea to decide whether or not to thin an ink when it is first taken out of the can.

Most modern inks are designed to be used on modern presses which are motor driven, and these presses will work the inks up quite well. This would not be the case on a hand lever press or a treadle press or a proof press with a hand inking system, so on these presses it is advisable to work the press for a while after inking it up, to let the ink reduce its body by itself, before a decision is made to thin the ink or not.

Thanks for your help so far. Rollers have been lightly set with a roller guage, indespensible i think. I am in the process of ordering new rollers for a veriety of reasons, but think the ones i have should give a reasonable result. In my early career we often used litho compatable inks to print on our heidelburg platens, but will need to review this perhaps.
I am thinking that the packing could be a bit soft, so will remove some and increase printing pressure.

I welcome any other comments as i am sure they will be helpful.

thanks again.

Thanks for your help so far. Rollers have been lightly set with a roller guage, indespensible i think. I am in the process of ordering new rollers for a veriety of reasons, but think the ones i have should give a reasonable result. In my early career we often used litho compatable inks to print on our heidelburg platens, but will need to review this perhaps.
I am thinking that the packing could be a bit soft, so will remove some and increase printing pressure.

I welcome any other comments as i am sure they will be helpful.

thanks again.

Thanks for your help so far. Rollers have been lightly set with a roller guage, indespensible i think. I am in the process of ordering new rollers for a veriety of reasons, but think the ones i have should give a reasonable result. In my early career we often used litho compatable inks to print on our heidelburg platens, but will need to review this perhaps.
I am thinking that the packing could be a bit soft, so will remove some and increase printing pressure.

I welcome any other comments as i am sure they will be helpful.

thanks again.

Most Offset-litho inks are suitable for letterpress printing without significant adjustment. For particular types of work, you may want more or less body to the ink. It sounds like your current ink may have insufficient body for the work you are trying to print. You certainly would not want to add oil to it if it’s already “squishing” at the edge.

Many formulas for commercial inks are designed for high-speed presses which require a bit less body.

John Henry
Cedar Creek Press

Since you have set your rollers with the gauge but are still getting a symptom indicative of rollers that are too low… is it possible that the chase isn’t sitting correctly and that’s causing the form to be too high?

if it’s really just that the ink is too “wet,” you could add a little magnesium carbonate to the ink. But that’s an extra nitpicky thing to do. ;D