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Re: [BKARTS] Papermaking

If you could only buy one reference book, I would strongly recommend Helen
Heibert's "A Papermaker's Companion". It's the best one on the market for
sound information and clear writing.

Roberta Lavadour
Pendleton, Oregon

----- Original Message -----
From: "Hal Truschke" <fineptg@xxxxxxxxxx>
To: <BOOK_ARTS-L@xxxxxxxxxxxxxxxx>
Sent: Monday, June 23, 2003 9:07 AM
Subject: [BKARTS] more photopolymer

> "Offset lithography plates are by definition flat (using the oil/water
> > resist described earlier). Sheets printed in this way will always be
> > flat. Photopolymer plates for offset lithography would not be an
> > exception."  --Don Drake
> That's right. Flexography or letterset are the correct terms for this type
of printing, but "dry offset" is a misnomer that is sometimes used. There is
a "waterless offset" process which uses a silicone coated plate. During
plate development the silicone is removed from the image area of the plate.
The ink adheres to the image area but not to the siliconized non-image
areas. No water is needed. The image areas sit slightly below the non-image
areas which creates a "well" to hold the ink. Another form of waterless
offset printing is gravure offset which actually etches the image onto a
plate which is inked, then surface ink is removed by a "doctor" blade.
National Geographic magazine is printed this way.
> The photopolymer that is used in offset printing is a light-sensitive
emulsion that coats the plate. Offset plates are made with a variety of
materials including aluminum (the majority of plates used), plastic, and
paper. Once an image has been transferred to the plate via a light source,
the polymer hardens. Photopolymer that is not exposed to the light is
removed. The photopolymer layer is very thin--these plates are quite
different from the photopolymer plates that are used in letterpress and
flexography printing. --h

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