Letterpress ink offsetting
I have had this recurring issue for over a year when (black) ink offsets onto back of cardstock (cotton and otherwise). It only occurs in bottom right corner with very small type (back of greeting cards). The offsetting is not always immediately obvious. Printing on Heidelberg Windmill black ball.
I thought it might be:
- too much ink, but doesn’t seem to be the case
- too much humidity, as it happens less in winter (dehumidifier running non-stop in summer)
- not enough humidity with ink evaporating after several hours and possibly becoming tacky
- something in the press wash; I’ve used standard wash, mineral spirits, baby oil (recommended by a fellow letterpress printer), Easy Street
- the rollers; I replaced them and it seemed to get better, but the next day back to the same issue
This happens so inconsistently I cannot pinpoint the cause. Today, for example, after checking all the variables, running a job just fine and adding the *tiniest* bit of ink after an hour I suddenly have issues.
What causes this? It’s totally slowing me down :(
PS: Also tried different black inks…
Possibly roller skid as it contacts the type, causing ink buildup on the edges of the type. Once enough ink piles up it will transfer to your work and offset to the next sheet. Try adjusting roller pressure or adding roller bearers to your form outside the print area.