At 1:02 AM -0800 1/1/00, Dave Bulger wrote:
>Date: Fri, 31 Dec 1999 08:39:34 -0600
>From: <dbulger@xxxxxxxxxxxxx>
>Subject: RE: OTRe: [OM] slide vs neg film - my take
>
>Gregg,
>
>Excellent description of the offset printing process!
>
>Note that while Gregg's explanation of the printing process covered
>magazines, books, etc., some of the high, high quality publications
>(particularly photos) were printed using a letterpress or photo-gravure
>process, where the plates putting the ink on the paper were physically
>etched or engraved with an acid type of "developer" to provide a physical
>separation between the areas to be printed and the areas not to be printed,
>as opposed to a chemical separation (offset printing).
Letterpress and photogravure are actually two slightly different categories
-- for regular letterpress, you make a plate with halftone dots like those
in offset printing, and the size and spacing of the dots (whose tops are
inked by a carefully calibrated roller) determines your image. (The plate
is etched so that everything but the printed parts is a fraction of an inch
lower than the rollers will contact.) For gravure, which is also sometimes
called intaglio, you make a plate where there a picture is represented by a
grid of tiny wells (usually 133 or 150/inch) of varying depth. The whole plate
gets inked, and then a blade wipes off all the ink, leaving only that in the
wells. The plate gets stomped onto the paper really hard so that all the ink
transfers.
What this means is that gravure, as opposed to halftone letterpress, is in
effect a continuous-tone process, since the amount of ink in each well
determines the darkness of that spot on the image. Under magnification you
might be able to see the grid, but there are no individual dots.
paul another guy with a misspent youth
Paul Wallich pw@xxxxxxxxx
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