(A copy of this message has been posted to the following mailing lists:
PRINTS-L and alt-photo-process).
A couple of years ago I participated in a workshop on a new and
particularly simple variant of the photogravure method. Although not very
impressed with my own efforts at the time, I nevertheless realized that
this new method had a potential which I wished to develop for my own
purposes. Now, two years later, I have invested in various apparatus and
materials, and some of the basic procedures and techniques have been
established. Therefore, however limited my present experience, I feel the
need to share it with a larger audience, which is the explanation for this
first appearance of mine on the Internet scene.
Being myself a b/w landscape photographer, my aim with the gravure process
is 1) to produce prints on 'real' paper, rather than on photographic paper;
2) to be able completely to control the color (or tint) of these prints;
and 3) to produce prints with a full range of values, particularly with
rich blacks.
The new photogravure method, which is based on photopolymer rather than on
copper as its substrate, was developed by the Danish lithographer Eli
Poinsaing, and is described in detail in his book "Photopolymergravure: A
New Method", Copenhagen: Borgen, 1995 (ISBN 87-21-00396-3, appr. $35.-;
written in both Danish and English). The basic elements are as follows:
=46irst a very fine stochastic raster, and subsequently a continuous-tone
positive, are contact exposed by UV light onto a sheet of photopolymer,
which consists of a thin steel base covered with a light sensitive nylon
resin; this resin is water soluble before exposure, and hardens - to
various degrees - after exposure. 'Development' of the 'plate' takes place
in plain water (about 20 dgr C); after a short soak the plate is gently
brushed with a so-called painting cushion, and finally sluiced briefly with
cold water. After drying and a final hardening UV exposure, the plate may
be printed as an ordinary copper etching. - Notice that no chemicals
whatsoever are involved in the preparation of the printing plate.
The theory of the process, which will be familiar to many, is that exposure
to the stochasic raster produces a fine network of lines which after
'development' - if no further exposure were to take place - will produce a
network of fine ridges with hollows between, in which the printing ink may
lodge and subsequently transfer to the paper. Wherever the positive
subsequently occasions additional UV exposure, the potential hollows will
harden to a greater or smaller degree, thereby producing variations in the
amount of accumulated ink, and thereby of tone in the print.
My equipment, besides regular photographic items, consists of a so-called
metal halogen UV lamp with a UV dosimeter, a self-constructed vacuum frame,
and a 60 cm wide printing press. The lamp has a 60 cm diameter reflector;
in order to control the effect of this diameter, diaphragms with holes of
various diameters were constructed to be placed in front of the lamp.
=46irst I wanted to establish the optimum exposure for the raster, i.e., the
exposure producing maximum black when printing the resulting plate,
possibly as varying with the aperture of the UV source; and the optimum
'developing' procedure. - It was found that aperture (and distance) of UV
source had only very slight effect on resulting black, which was achieved
for about 400 (arbitrary) units of exposure. Optimum development was
initially found to consist of 1 min soak followed by 4 mins brushing. This
was established for small pieces of polymer; it was later found that for
larger pieces, a 4 min soak followed by a 1 min brush, again followed by a
4 min soak and a 1 min brush, provided a method practically insensitive to
size of printing plate.
After that, influence of UV source aperture for exposure of positive was
examined; again only the subtlest, and quite possibly non-reproducible,
differences were found.
By using a step wedge as positive it was found that difference between the
'white point' and the 'black point' amounted to about 3.7 stops, requiring
quite a considerable increase in contrast from an ordinary 'paper-bound'
landscape negative. This, however, concerns straight photographic
procedure, and thus probably should not be covered in this forum.
As far I have printed only two images. One is printed from an already
existing 4x5" positive of details of a stop watch (made several years ago
for other purposes), while the other has been produced from a 24x30 cm
positive derived from an ordinary 4x5" landscape negative. The latter
positive caused some trouble producing, as the required increase in
contrast amounted to a factor of about 10. The resulting print, however,
fully captures the span of values from (almost) white to a velvety black,
and in some ways represents an improvement over the corresponding
photographic print.
In conclusion I can say that the production of the printing plate (and the
printing of it) has proven a very simple and straight-forward process. The
problems I have encountered have in the main been with the production of
the required positive; and these difficulties I expect to have surmounted
in the very near future. I therefore do not hesitate recommending this new
photogravure process to anybody with a need to produce 'real' paper prints.
- And a Happy New Year to everybody!
Strange
Strange Ross
Hvidehusvej 35
DK-3450 Aller=F8d
Denmark Phone: (+45) 48 17 42 92