Pigment Printing Processes

The title refers to the image which is composed of light-insensitive pigment rather than silver produced by the photographic process. Though the pigment is generally referred to as carbon other dyes and pigments were also used. The processes are generally based on the reaction of bichromated colloids (usually gelatine with potassium or ammonium bichromate) to light:

• When exposed to light bichromated gelatine becomes insoluble, the unexposed areas remain soluble in warm water.
• Unexposed areas expand in cold water.
• Greasy ink will adhere to insoluble areas whilst being repelled by damp soluble areas.
• Gelatine in the presence of a bichromate becomes insoluble when in contact with metallic silver.

Pigment processes offer a wide variation of image rendition, from the representational, practically indistinguishable from silver prints, to 'control' processes where each print is unique and shows artistic manipulation in its production. Some of the processes allow the photographic print to be reproduced in short print runs in a press; an intermediate step to related photo-mechanical processes.

Mungo Ponton was the first to recognise the light-sensitivity of potassium bichromate in 1839.¹ Robert Hunt introduced the Chromatype process in 1843 which used copper sulphate and potassium bichromate on paper. The sensitivity of bichromated gelatine and its insoluble nature when exposed to light was discovered by W.H.F. Talbot and included in an important patent of 1852.²

Carbon

The Carbon process originated with work by Poitevin (1855) but it was not until 1864 when J.W. Swan published his working method that a practical process became available that could be operated by the amateur and was systematic enough for commercial use. Permanent photographs, as carbon prints are, was a topic that was much discussed in the press of the period and several photographers were working in this area, at the time all pigment processes were grouped under the title of carbon prints. The search for a permanent printing process was given impetus by a prize offered by the Duke of Luynes.¹

Poitevin

Alphonse Louis Poitevin's patent of 1855 mentions two working methods:

• Based on the ability of insoluble (exposed) gelatine bichromate to take up greasy ink. The finished print could either be the inked gelatine itself or the gelatine could be used to transfer the image to paper as in a lithographic process.
• Adding pigment to bichromated gelatine and washing away the soluble parts after exposure.

The patent mentions the ability to apply different colour pigments to different parts of the print. The materials mentioned are albumen, gelatine, gum arabic or fibrine in conjunction with a chromate or bichromate.²

Testud de Beauregard

In this process the pigment was dabbed on the bichromated gelatine in a similar way to inking type in a press.³

Pouncy

This was the forerunner of the gum process in that gum arabic was used in place of gelatine. Pouncy announced his process without giving details, a collection was started by the Photographic Notes magazine (Thomas Sutton) to purchase the process for £100, subscribers would receive details of the process on paying their subscription. Before the money was raised the patent was abandoned and therefore published, which must have deterred further subscribers. The editor pointed out that the patent only gave the general principles of the process without its method of working and that the subscriptions should continue (the asking price seems to have been reduced to £50 around this time). In the meantime Pouncy's prints that were exhibited came in for a lot of criticism, the promised detailed instructions given to subscribers amounted a to a single sheet of paper and specimen prints were described as poor. Pouncy's cause was championed by the Photographic Notes whilst sarcastic articles appeared in the rival Photographic News magazine. Pouncy's process should have been treated for what it was - an early attempt at producing permanent prints - rather than a finished product as promoted by Pouncy and Sutton (who was inclined to get carried away with ideas).⁴

Garnier and Salmon

Henri Garnier and Alphonse Salmon developed a dusting-on process using iron citrate. The process depended on iron citrate becoming non-hygroscopic when acted on by light and on the adhesion of carbon powder to moistened iron citrate unmodified by light. A very strong solution of iron citrate was coated on a sheet of paper, placed under a positive print and exposed to light. On removal from the printing frame the paper was dabbed with carbon powder at the same time as breathing on it, the carbon powder would attach itself to the unexposed parts. Dipping in water would remove the unaffected citrate of iron.⁵

Laborde

Early prints lacked detail in the half-tone areas. The cause of this was that the gelatine, which was mounted on a paper support, became insoluble when exposed to light starting at the surface i.e. furthest from the paper support. The soluble gelatine that should be washed away was, therefore, trapped against the paper, also, small areas insoluble to a shallow depth were washed away. The Abbé Laborde gave the reason for the lack of half-tones in 1858.⁶

Bennett

To remedy the problems of the lack of half-tones, J.C. Bennett proposed (1858) exposing the gelatine through the paper support.⁷

Fargier

In Adolphe Fargier's process the bichromated gelatine solution was coated on glass and exposed, the surface was then coated in collodion and the plate put in hot water to dissolve the soluble gelatine, the glass would also detach at this point, the gelatine was then mounted on paper and the collodion dissolved. This was the first mention of transferring to a temporary support.⁸

Swan

J.W. Swan's process was important not for its originality, which was negligible, but for providing an end-to-end working method that could be followed by the photographer using commercially available materials. Swan's early description of his process was different to that later employed, in a paper read before the London Photographic Society in early 1864 he describes the gelatine film being coated with collodion to provide support (the two together were referred to as a tissue), the exposure was made through the collodion thus allowing the soluble gelatine to be washed away. The tissue was mounted on a paper support (collodion side down) during development after which the print was finished and could remain on that paper or be re-mounted on another sheet of paper (gelatine face down), the print would then not be laterally reversed. Swan's patent was purchased by the Autotype Company in 1868 which supplied materials and undertook printing.⁹

Johnson

John Robert Johnson, of the Autotype Company, introduced improvements including the double transfer system.¹⁰

Abney

William de W. Abney noted that following exposure once the insolubility process had started the bichromated gelatine would continue to harden even in the dark.¹¹

Using the Carbon Process (Autotype Co. version)

The image comprises a pigmented gelatine sheet that varies in depth in proportion to the tones of the negative. Unexposed gelatine is washed from the print.

There were two versions of the process - single transfer and double transfer - in the first the tissue was mounted on a support while being developed and remained on that support, the finished print was laterally reversed. In the double transfer version the tissue was mounted on a temporary support whilst being developed and later mounted on its final support, the print was laterally correct. The single transfer, double transfer and temporary support papers were all different. The tissue was the same for both versions and comprised a coloured layer of gelatine on a paper support. Carbon tissue was available in a wide range of colours, the transfer paper was also sold in different tints and finishes. Carbon prints could be mounted on other final supports such as metal or ceramics and glass as diapositives.

The carbon process had many minor variations especially in the transfer paper used. The following outline of the process is from the mid 1900s.

Sensitising

Tissue was available either sensitised or unsensitised. To sensitise tissue it was immersed in a solution containing potassium bichromate and allowed to dry.

Printing

The tissue was printed under a negative in a printing frame. As there was no visible image an aktinometer was used to judge the exposure. It was important that the negative had an opaque border that would produce a clear surround to the finished print, a mask could be used in the printing frame.

Development - Single transfer

The transfer paper was soaked in water and put face up in warm water, the tissue paper was put in the same warm water face down over the transfer paper. On removal the two were pressed together and then placed in hot water. Once gelatine started to run from the tissue the original support paper could be lifted from the tissue. The gelatine was then able to wash out from the tissue. When no more gelatine came from the tissue the print was rinsed and put in an alum bath to remove the yellow bichromate stain. It was then dried as a finished print.

Development - Double transfer

The process was the same as for the single transfer method except that the tissue was mounted on a temporary support paper while being developed. The temporary support was gelatine coated paper which was waxed prior to use. After development and removal from the alum bath the print was dried and then soaked in cold water along with the double transfer paper. The print and the double transfer paper were brought together in a bath of warm water. After removal the print was dried and the temporary support paper pulled from the print.

Ozobrome, Carbro

Carbro, and the similar processes listed here, are carbon prints produced by contact with a bromide print or other image. Its origin goes back to the Mariotype process but it was only with the introduction of the Ozobrome process that 'carbon by contact' became popular. Ozobrome was developed by Thomas Manly in 1905, the name Carbro was introduced in 1919 when the process was improved by H.F. Farmer.¹

The improved method consisted of soaking a gelatine silver bromide print in water and a sheet of carbon tissue in a bath containing potassium ferricyanide, potassium bromide, potassium bisulphate and potassium bichromate. The two were then put in contact where the gelatine of the carbon tissue became insoluble where it was in contact with the metallic silver of the bromide print. The tissue, separated from the print, was then treated as an ordinary carbon print. Alternatively the tissue could be developed whilst still on the bromide print rather than mounting on transfer paper, the bromide print could be re-developed producing deeper tones in the finished carbro print. Multiple carbon tissues could be mounted on a single print. Where the bromide print was separated from the carbon tissue it could be re-developed and used to produce more carbro prints.

Smaller negative sizes were coming into use in the 1900s and as a bromide print was used it was easier to produce large prints than compared with the carbon process where intermediate negatives would be needed. Bromide prints could be printed by artificial light and the carbro tissue required no exposure at all allowing the amateur photographer to work in the evenings - an important consideration at a time when an increasing number of amateurs were taking up photography. The carbro process was popular for producing colour prints from three-colour separation prints.

The quality of the carbro print was very good with only very slight lateral diffusion at the soluble/insoluble borders. Materials were sold by the Ozotype Co.

Mariotype

In 1873 A. Marion published details of his Mariotype in which, as he described it, the transfer paper containing gelatine was sensitised with potassium bichromate and exposed under a negative. The transfer paper and a sheet of pigment paper were put in a bath of potassium bichromate and brought together. When withdrawn they were kept in contact for 8 - 10 hours, the pigment paper had then become selectively insoluble and could be developed in warm water. The finished print was not laterally reversed.²

Fargier's iron salts process

Fargier's process of c. 1874 used paper coated with iron perchloride and citric acid exposed under a negative. The paper was then coated with pigmented gelatine or gum containing potassium bichromate. The gelatine became insoluble where it was in contact with light-affected perchloride. No use was made of the process.³

Ozotype

This was introduced by Thomas Manly in 1898 as an alternative to the carbon process, it had the advantage that a transfer to another support did not take place. Paper with a gelatine coating was sensitised with a bichromate and a colloid. The paper was exposed under a negative and washed to remove the unaffected salts. A pigmented gelatine sheet was placed in a solution of copper sulphate, acetic acid, glycerine and hydroquinone. The print was added to the solution and brought together with the gelatine sheet, they were then taken from the solution and left in contact for some time. The two were put in hot water where the backing paper attached to the gelatine sheet could be removed and the unaffected gelatine washed away.⁴

Gum Bichromate

The gum process became popular in the 1890s. It gave the photographer a lot of control over how the print looked, to the extent that some prints do not resemble photographs at all.

Working methods and formulae varied but in outline paper was coated with a solution containing gum arabic, a bichromate and pigment (usually water colour). This was then exposed under a negative, the gum becoming insoluble in proportion to the light reaching it. The print was developed by dissolving the still soluble gum in water. Development could be brought on or retarded by the use of brushes or sponges etc. Multiple printing (on to one finished print) was possible, either from the same or different negatives. Different colour pigments could be used for each printing. A variation was to coat the gum mixture onto an already developed platinum print.

Oil

The origins of the process go back to Poitevin (1855). However oil printing as a control process for photographic prints started with G.E.H. Rawlins in 1904. The process could be adapted into a photo-mechanical process (oil transfer) by pressing the finished print into contact with ordinary paper.

Gelatine coated paper was sensitised with a bichromate solution and then exposed under a negative. After exposure the print was soaked in cold water, the water was held by the gelatine unaffected by light. An oil based pigment was dabbed or brushed onto the surface, this was repelled by the water-logged gelatine but held by the insoluble gelatine.

The oil process was very flexible leaving scope for the photographer to develop a particular style of printing. Pigments were available in a wide range of colours, multi-toned prints were possible by applying pigment locally. Parts of the print could be strengthened by applying extra pigment, brush marks were sometimes deliberately introduced. The gelatine coated paper and pigments were available commercially.

Bromoil

This process enabled oil prints to be produced from bromide enlargements, the gelatine contained in the bromide print forms the image rather than being a separate sheet to which the image is transferred by contact. The origins of bromoil probably lie in a patent by E. Howard Farmer.¹ Bromoil, though, came about from a suggestion by E.J. Wall in 1907 and was developed practically by C. Welborne Piper that same year.

A finished bromide print was put into a bleaching bath containing potassium bichromate.² This removed the visible image and selectively hardened (made insoluble) the gelatine in proportion to the silver image. The image was then placed in a fixing solution (hypo). The print was inked up as in the oil process.

Oleobrom

This is a variant of the Bromoil process developed in the Ilford laboratories by F.J. Shepherd and sold under the Wellington & Ward brand from 1931.

Oleobrom was easier to use than Bromoil giving more consistent results, the bleaching procedure was improved and standardised, special Oleobrom paper was required. The main difference, in use, was that the print was inked up by a roller rather than brushes. Part of the inking procedure was carried out with the print immersed in water.

Summary of the Oleobrom process:

• Develop the print.
• Place the print in the stop bath for two minutes.
• Rinse the print for two minutes.
• Bleach in the Oleobrom bleacher.
• Wash for three minutes.
• Fix in hypo for ten minutes.
• Wash for between 30 minutes and one hour.
• Dry.
• Ink dry on cork mat.
• Immerse in water and roll.
• Remove print to cork mat and re-ink.

Oleobrom outfits were sold in sizes from half-plate to 15" x 12". These contained: 4 rollers, 2 ink palettes, cork mat, rubber sheeting, Oleobrom retouching pad, spotting stump, pigment, bleacher, stop bath.

Trichrome Carbro

The Autotype company was the leading supplier of carbon and carbro materials. The Trichrome process is the adaptation of the Carbro process for three-colour work producing prints or transparencies.

The process uses bromide enlargements from red, green and blue separation negatives. Each bromide print is placed in contact with a pigmented gelatine sheet, coloured cyan, magenta and yellow, (referred to as pigment paper or carbon tissue). During the process the gelatine sheet is sensitised with potassium bichromate making the gelatine insoluble after contact with silver.

Outline of the process

• Bromide prints are produced from three-colour negatives (red, green and blue). It was important to ensure that the bromide print did not have an additional gelatine coating.
• Pigment paper, which was pigmented gelatine attached to a paper support, was sensitised by soaking, separately, in the A and B solutions.
• The pigment paper was placed in contact with the appropriate bromide print and left for 15 minutes. The 'red' bromide print was matched with the cyan pigment paper, the 'green' print with the magenta paper and the 'blue' print with the yellow paper. On separating the two, the image on the bromide print will be found to have been bleached and no longer visible, it could be recovered by re-developing the print. The sensitised gelatine becomes insoluble in proportion to the silver in the bromide print, i.e. shadow areas in the print will produce a thick layer of insoluble gelatine.
• The pigment paper was then placed on a waxed celluloid sheet (with the surface previously in contact with bromide print next to the celluloid).
• The celluloid and pigment paper were placed in warm water to 'develop' the image, the paper support could be removed and the soluble gelatine would dissolve leaving an image consisting of pigmented gelatine of varying thickness.
• The above was carried for each of the three prints.
• The three images were then mounted on a single temporary support (gelatine coated paper). The order of mounting on the temporary support was cyan, magenta and yellow. The use of a temporary support was to give the correct left-right orientation in the final print. After attaching each image to the paper support the celluloid support (to which the pigmented gelatine was still attached) was removed.
• The last operation was to mount the images on a final sheet of paper (single transfer paper), which leaves the cyan image on top.