Blobby printing

See linked photos:

Printing on my SP-20 this morning, using oil-based Blue 072 straight from the can. It’s warm – about 85° F – in the studio. Humidity isn’t too bad, about 55%.

The ink is really blobby. In adding more ink to get it up to the right color, it got very goopy and runny. Is this the heat? I tried adding some corn starch on press, but that just knocked the color back and didn’t seem to do much for the printing quality.


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Forget corn starch, use magnesium carbonate. It’s available from several sources, including Graphic Chemical.

Yeah, I think the corn starch made it worse. Interestingly, after I cleaned up and re-inked, when I tried some Lettra, the print was much better quality. On the Arturo 110 lb. that I’m using for the job, the ink spread a lot more. I soldiered on and made the best of it.

Another thought is, two hits of thinner ink instead of one hit of lots of ink. Mag will help too but only so much.

I assume this is from a photopolymer plate. I think it looks like your plate might be halftoned (screened). You might have had the color set to a percentage instead of solid. Go back and look at your digital design and see if you did that. It is an easy mistake to do, but often hard to see on the computer if you are doing it in a dark color. You might have it set to something like 60% black.

No, the plate was set to 100%. I think the addition of corn starch caused the speckles. I’m ordering some mag carb and will try that next time.

Occasionally I am getting the same printed effect. If I leave the ink on the press, after a while I can see the same effect in negative on the form rollers ( very small bare spots ).
I feel that it is some chemical incompatibility making the solids in the ink clump together. Sometimes I wash the rollers on-press with Unigraph UNI O.D.. I was warned to wash it off really well. Perhaps some of it stayed behind in the pores of the rollers. Sometimes I suspect Smooth-Lith to be the culprit. I use soy based form ink adjusted with low tack opaque white, and California wash to clean the rollers.
If I remember well it usually happens with brown colours.