Offset Printing - Printer's Hickey Question

I need some help before I make a mistake in an article I am writing.

I have heard that the round flaws called printer's hickeys on offset printings are caused by a small piece of foreign matter (dust or whatever). Specifically I thought I had heard that the foregn matter was on the plate (and thus was transient). But knowing a bit about the optical lithography process that used to be used to make stamp plates, I am wondering if it isn't foregn matter on the plate, but instead foreign matter somewhere in the optical system or on the original image being projected onto the resist on the plate, and thus something that actually becomes part of the finished plate image.

I have regularly encountered hickeys in offset printing during my time as a print and production manager for HSBC Bank. Everything that I have ever been taught indicates that they are foreign matter that adheres to the plates post plate production.

This is confirmed at a website that I like....
http://offsetpressman.blogspot.co.u...on-your.html

Hope this helps, and good luck with the article.

GLENN

". . . they are foreign matter that adheres to the plates post plate production."

Agree.

Isn't there a clue to this question in the colorless circle around the hickey (also known as donuts, no?)? The physical attributes of the foreign matter stuck to the plate interferes with the uniform inking around it, resulting in the donut-like image.

I always understood that the particle was on the rubber offset-cylinder that got pressed in a bit giving way to the "halo" around it...

The particle may stay on the rubber cylinder for quite a while! I have seen stamp booklet covers that had it during the entire production and so you could even see it moving up a bit!

Gale - so you are saying it might not be on the plate but on the offest tranfer cylinder?

BTW, I have heard this sureface called a "blanket" (by someone who worked for Babknote Corp of America), which doesn't suggest rubber to me - in fact I recall sseing one at a show and again I didn't come away with the mpression it was rubber..

Here is a definition of a hickey from my copy of Production for the Graphic Designer by James Craig (Watson - Guptill Publications, 1974).
Hickey - A defect, or spot, appearing in the printed piece. Hickies are caused by dust, lint, or bits of ink skin on the printing plate, the type form, or the blanket (in offset) and show up as specks surrounded by a halo effect.

In other words, the schmutz can adhere almost anywhere during the printing process. The end result is the same. Schmutz happens!

Thanks everyone!