Explaining

How they were produced

How Photochromes were produced

Photographs were taken in black and white, then hand coloured in detail to details noted by the photographer and then a process using up to 19 stones was used to print them.  We don't know the exact details of the process, this has been lost over time, although we have worked some of it out.

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 states.

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 four stones and as many as nineteen  stones might be used for a given 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 re-ground 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 having access to a range of originals that have been in private collections and up to owned by  Adam Aaron Studios, had 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.

Cotswold Pictures Ltd have very detailed scans of original prints, in some cases several sets, as well as photographs we have commissioned from some we have access to. We have then used photographic editing techniques to roll back the damage of time and bring the images as near as possible to how they feel they would have originally looked, but with some improvement in detail that our printing processes now allow. Produced as limited edition quality works of art, on a fully colour managed system utilising materials  of archival standard throughout, these fine works will last longer than any of us, becoming not only fine works to enjoy but heirlooms to hand down through future generations.

Perhaps is another hundred years or so, someone will be asking how we produced our works to such a high standard compared to that which is generally available today. our images together with those of Camera Images are likely to be some of the only images being produced now that will still be in mint condition by that time