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Houses of
Parliament, London
Castle Douglas,
Dumfriesshire
Dublin, Ireland
Caernarfon
Castle, Wales
Monmouth Bridge,
Monmouthshire
Glencoe, Antrim,
Northern Ireland
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How they
were produced - a more in depth look
We know a little of
how the images were produced from working notes that have survived
and copies in various development stages.
The process was
developed by a Swiss Chemist, who spelt it Photochrom without the
trailing 'e', when taken up (licensed) by the
Detroit
Photographic Company in the USA
the 'e' was added becoming Photochrome, it was marketed around the
world, with images produced covering very many countries. Most of
the images in our collection were either by the Detroit
Photographic
Company, or by Photochrome Zurich
(aka Photoglob Zürich), stamped with the characteristic caption in
gold lettering along the base of the print, with a serial number and
"P.Z."
A process that we
don’t now understand fully, was used to print them using between 4
and 19 stones. It is thought that the process was as follows:-
The photographs
were taken in black and white and the photographer made a very
detailed sketch showing all the colours in the scene. These were
then expertly hand coloured. The method of transferring a
hand-coloured photograph to multiple printing plates uses separation
negatives, one for each colour. The colorized original is
re-photographed through different coloured filters onto black and
white negatives, one for each colour. The negatives are then
transferred onto the printing plates. Up to twenty colour
separations might be produced for one Photochrome lithograph print. An example survives of the company’s postcard proof sheets from
about 1900 showing the progression from black ink to nine colours
in these examples
The stones
used by the Detroit Photographic Company were imported from Bavaria
and coated with a special Syrian 'asphaltum' substance that would be
chemically sensitized to light, put in contact with a photographic
negative, exposed to the sun for up to several hours, then
developed in oils of turpentine.
The areas of the very thin asphalt gel most exposed to light would
harden, becoming insoluble, the less exposed residue would be washed
away. Tonal values of the remaining positive image could be
manipulated by varying the chemistry and development times.
Technicians could do the equivalent of burning and dodging by
retouching the brush and polishing with fine pumice powder. The
final steps in preparing the stone were an acid etch to bond the
remaining image with its very fine grain, and a glycerine bath.
A separate stone would be made for each colour to be used. A minimum
of 4 stones and as many as 19 stones might be used for a
single image. A transparent ink would be applied to the stone, then
transferred to high quality paper, whose texture resembled the smooth
photographic printing paper of the day.
The final step was a varnish which gave each print added depth and
richness. Because the process involved a number of crafts people and
because the stones had to be reground occasionally, substantial
variations can be seen between different editions of the same image
over the years.
We have been able
to see the variation between original Photochromes, as we have at
least two scans of most of the images from different sources and
have access to a number of originals.
Luckily we have access to a
range of originals, that have been in private collections, have been
kept away from light in archival conditions so they they have been
kept in near mint condition. At least some having been presentation
images owned previously by an ambassador, and well looked after are
probably the finest and highest quality ever produced, and still in
near mint condition today.
Camera
Images' GBpictures archive have very detailed scans or photographs of
original prints, in some cases several sets, and they have allowed
us to put all of the images we have available here, available under a
Creative Commons Licence so you can use these images.
We are
still adding to this archive and if you are lucky enough to own any
Photochromes what we have not included so far, we would love to be
able to photograph and include yours as well. |
