Digital BW, The Print

----- Original Message -----
From: "Paulo Baptista" <paulo.baptista@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Sunday, September 22, 2002 12:53 AM
Subject: Re: [Digital BW] RE: Photogravure and Inkjet


> Hi all,
>
> an useful source of info on photogravure and other antique printing
> processes can be found on the book "The Keepers of Light", by William
> Crawford (Morgan & Morgan, 1979). Also Aperture, Inc. (www.aperture.org)
> publishes several series of photogravure prints by photographers such as
> Paul Strand, Alfred Stiegliz and others, produced by the Photogravure
> Workshop, located in Hadley, MA, and supervised by master printer Richard
> Benson.
> As far as I know, the photogravure process uses variable depth etching on
a
> copper plate (instead of a halftone screen), through a high pressure
> printing press to produce a grayscale print with oil inks on fine art
papers.
>
> Regards,
> Paulo Baptista
> www.paulbaptista.cjb.net

There are several versions to create the copper printing plate, one of them
uses an aquatint like screening
by burning in resin particles on the plate and cover that plate then with a
photo sensitive coating (Kodak, Autotype, Kiwo). Exposure through continuous
tone film. The layer thickness differences of the coating after development
(rinsing with water) influences the speed the etching fluid gets to the
copper and starts biting away the copper. Then all is cleaned afterwards and
an irregular pattern of different sized naps (cells) is visible. The best
way would be that the depth is varying but the other proportions of a nap
will also get bigger as well. Nifty systems where the plate is attached to
the top of an etch chamber, and etch sprayed on it from below can control
that behaviour and so can different etches.

More industrial methods of conventional photogravure used the same
continuous tone film and sensitive coating but introduced an extra graphic
film in the exposure (or exposures) with a brickwork like screen raster
(several varieties exist) instead of the resin dust burned in. A Tjech named
Klietsch invented most of the old rotogravure . Kurtz and Levy in the US and
Swan the English inventor (light bulbs too)  and founder of the Autotype
company are the other names usually mentioned in photogravure. Didn't check
the names so all IIRIC.

I have mentioned the Hell computer controlled engraving of copper cylinders
already. At first an analogue system with direct scanning of continuous tone
film and simultaneous engraving of the cylinder with a steel bit. This
became more digital through the years. The screen is half-autotypic as the
surface size of the naps is also varying, tone control is easier then. Later
on other methods of engraving with laser etc. beams were introduced.

An interesting technic appeared in the late seventies. Crosfield Electronics
of scanner fame was involved. A copper cylinder with the brickwork like
screens in them already etched and filled again with a resin that then was
burned out by a computer controlled laser. What was removed by the laser per
nap then was filled with ink while printing. After the printrun all the
resin is melted out and the cylinder naps refilled with resin again. That
had the advantage that no new copper layer had to be applied, turned and
polished for every printrun like in the other processes. It didn't stop the
decline of rotogravure however.

Ernst