Calotype and other early paper processes

Photogenic Drawing

Photogenic drawing derives from experiments started in 1834 by W.H.F. Talbot, the process was made public in January 1839. It was the first negative/positive photographic process, the negative aspect was largely replaced by the calotype, the positive part of the process continued in use with the calotype and on into the wet collodion period. The negative could be produced in a camera or by simply placing objects on the sensitive paper (what would later be called a photogram). The process was not patented. Talbot also experimented at this time with silver iodide and silver bromide in place of silver chloride.¹

An early manual for the process was produced by the print seller Ackermann in 1839 and supplied with his Photogenic Drawing Box. The stages as described in Ackermann's manual were:

Preparing the paper

Writing paper was dipped in a solution of sodium chloride (common salt), partly dried and then coated with silver nitrate (forming silver chloride). The paper was dried, given another coat of silver nitrate and again dried. For greater sensitivity the paper, once dry, could be coated more than once. It was recommended that when multiple coats were given a narrow strip of paper was cut off and exposed to light, to allow the sensitivity of the paper to be judged.

Exposure

Photogenic drawing was a printing-out process so exposure was continued until the correct tone had been reached.

Fixing

The image was washed and fixed by immersion in either a solution of common salt, potassium iodide or sodium hyposulphite. It was then dried. Common salt was recognised as stabilising the image, for a permanent print it was recommended that potassium iodide or sodium hyposulphite was used.

Producing the positive print

Sensitive paper was prepared as for the negative, it was then placed in contact with the negative in a printing frame (called a reversing frame) and exposed to daylight. The resulting positive print was then fixed as for the negative. This stage might be omitted if the photograph was not produced in a camera i.e. it was a photogram or drawing on glass.

Ackermann's manual also showed how photographic prints could be made that resembled sepia drawings and line engravings by applying either an opaque or semi-opaque coating to a glass sheet and using an etching point to remove the coating or overpainting to create highlights. Prints were taken from the glass in the normal way.

Plain Salted Paper (Salt print, Silver chloride paper)

Plain salted paper was a term used to describe positive prints made using the photogenic drawing process irrespective of the negative process used. They were largely replaced in the 1850s by albumen prints. 'Salt print' is now commonly used to describe this type of print.

An excess of silver nitrate was present which reacted with the small amount of organic material in the paper present as part of the sizing process. No additional starch or gelatine was added when preparing the paper. The size used on French papers was generally starch based which produced different results to English papers that were mostly sized using gelatine.

Salt prints have a matt finish and as there is no gelatine or albumen layer on the paper the image appears to be within the fibres of the paper. The colour of a salt print differed mainly as a result of the fixing process, where salt was used the finished print tended to have a lilac or mauve colour, where hypo was used the colour was generally a reddish brown. The colour, though, could be modified, for instance by placing a hot iron against the print or by sulphur toning using old hypo. Gold toning was used from the late 1840s and was common a few years later.²

Calotype

The calotype process was developed in 1840 by W.H.F. Talbot and patented in 1841.³ The process covers the creation of paper negatives, the positive which was not part of the process was typically produced by the existing salt print method. The primary difference between the calotype and the earlier 'photogenic drawing' process was the greater sensitivity of the paper and the development of the latent image by the use of gallic acid before and after exposure. Exposure times with the calotype were much shorter than with the photogenic drawing process making them comparable to those of the Daguerreotype.

In Talbot's original specification there were five stages to the process:

Iodising

Writing paper was washed with successive solutions of silver nitrate and potassium iodide, being dried after each wash. Opinions differed as to which wash should be applied first. In this state the paper could be stored.⁴

Sensitising

The iodised paper was washed with 'gallo-nitrate of silver', then washed in water and dried. Gallo-nitrate of silver was a mixture of two solutions: silver nitrate, distilled water and acetic acid (called aceto-nitrate of silver) and, secondly, gallic acid in distilled water to which alcohol was sometimes added. This was an unstable mixture that was prepared immediately before use. In this state it was best to use the paper within a few hours though it could be kept for longer.

Exposure

This produced only a latent or faint image. Slides for paper processes were generally of the double pattern, holding two sheets of paper, and opened like a book for loading. Glass was placed in front of the paper to flatten it, so the exposure was made through the glass. Blotting paper was used to separate the two sheets of paper. Less common was to stretch the paper over the front of the glass and glue it at the back.

Development

On removal from the camera the image was developed (the term 'brought out' was often used) by washing the paper with gallo-nitrate of silver in a warm environment. As the paper was sensitised with gallic acid, which was a developing agent, calotypes could self-develop if left for many hours.

Fixing

The paper was dipped in water, partly dried and then washed with potassium bromide, it was then washed with water and dried.

In his second patent Talbot advocated the use of a hot solution sodium hyposulphite (hypo) to clear the yellow stain on the image caused by the iodide and as an improved fixer. He also recommended melting wax over the negative to increase its transparency. The use of hypo as a fixer was not original so it is not clear why it would be included in a patent.

Talbot did not publish a manual for the process, early working instruction were given by W. Raleigh Baxter in a small book published in 1842 and by George S. Cundell which was published in the Philosophical Magazine (1844) and reproduced in A Manual of Photography by Robert Hunt. These closely followed Talbot's patent except that Cundell added common salt to the iodising solution. A modification that appeared a few years later was the use of 'silver double iodide' as the iodising solution. This was produced by mixing potassium iodide and silver nitrate, the precipitate from this (silver iodide) was washed and then dissolved in potassium iodide. This solution was coated on the paper in a single wash rather than separate coats of potassium iodide and silver nitrate.⁵

Specialist paper for the calotype and salt print processes was sold by R. Turner, Chafford Mill, and J. Whatman, Turkey Mill. Paper was also available pre-iodised and pre-sensitised. An advertisement for pre-sensitised paper states that it will keep for between 14 and 20 days.⁶ All of the chemicals required for the process were readily available and, where possible, prepared as ready-to-use solutions e.g. silver double iodide, aceto-nitrate of silver.

The image on the right has the watermark "R Turner Patent Talbotype".

The calotype in use

The calotype process was not as widely practised as it should have been; due in part to the requirement to purchase a licence, even by amateurs. Other factors also affected its use, one being the recognition that prints were prone to fading, another was the lack of promotion through an easily available published manual.

The process could not compete with the Daguerreotype in the commercial portrait market where the minute detail shown in the Daguerreotype proved captivating. Licence restrictions prevented a critical mass of amateur photographers from forming; it is they who would have turned to landscape and architectural subjects that were most suited to the process. Relaxation of the patents, except for commercial portraiture, in 1852 led to greater use but this was at the start of the wet collodion process.⁷

One who did try commercial portraiture was Henry Collen who took out the first professional licence in 1841. The Chemist for 1842 gives the portraits on show a very good review noting that it takes only a few seconds exposure.⁸ Claudet, after protracted negotiations, also took a licence (summer of 1844) to operate the process but negotiations with Beard came to nothing.⁹

Blanquart-Evrard Negative Process

This was a modification of the calotype process, introduced in the late 1840s. The paper was salted with both iodide and bromide before coating with silver nitrate, the important difference between it and the calotype was that gallic acid was not included at the sensitising stage. Development was by gallic acid. The process was used extensively on the continent and was considered better than the calotype especially in hot climates.¹⁰

Blanquart-Evrard Positive Process

This was the first application of development of the latent image applied to positive prints (developing-out process). The process was introduced around 1850 and consisted of the following stages:¹¹

Preparing the paper

The paper was immersed in a weak gelatine solution containing potassium iodide and potassium bromide. It was then dried and subjected to the vapour of hydrochloric acid, dried again and immersed in a solution of silver nitrate to which a few drops of nitric acid had been added. The excess silver nitrate was removed with blotting paper.

Exposure

The paper was exposed under a negative for a few seconds.

Development

The print was developed in gallic acid for around 20 minutes.

Fixing and Toning

The print was immersed, without washing, in hypo to tone the print (sulphur toning) and then fixed by immersion in a second hypo bath. It was then dipped in hydrochloric acid, washed and dried.

The paper, recommended by Sutton for positive prints, was Canson's. The use of gelatine at the preparation stage provided a barrier between the image and the paper and provided the necessary organic material, it also gave a smoother surface for the image. The process underwent some modifications, the sulphur toning step was quickly replaced by gold toning. Sutton details (in 1856) a process using barium chloride as the salt and omits the hydrochloric acid step. In the second edition of 'The Calotype Process. A Handbook to Photography on Paper' Sutton lists a printing-out rather than a developing-out process, gelatine was used when preparing the paper.

Several reasons were given for this rather complicated process:

• The short exposure time reduced the overall time to produce a large number of prints when worked in a mass production environment.
• The process produced prints that were more permanent than ordinary salt prints and less likely to fade.
• The colour of the print tended to vigorous purple/brown or purple/black with clear highlights which was more attractive than the red/yellow hues of salt prints. The salt used in preparing the paper affected the colour of the print.

Unsurprisingly amateurs did not embrace the process and largely continued to use plain salted paper or the recently introduced albumen paper.

Blanquart-Evrard established a printing works at Lille (1851) to exploit the process and with Thomas Sutton set up a printing works in Jersey (1855) - The Establishment for Permanent Photographic Printing. On a visit to Lille, Sutton records that 250 prints were produced from a negative in under two hours. Neither establishment remained in business for very long. The developing-out of positive prints was then largely forgotten until later in the century.

Wax Paper Process

This was a modification of the calotype introduced in 1851 by Gustave Le Gray. The paper was impregnated with wax prior to sensitising, in the calotype, wax was coated on the finished negative. The process proved very popular replacing the ordinary calotype process. Details of the process differed especially in the salting chemicals used, Robert Hunt (1854) lists the following steps:¹²

Preparing the paper

Paper (Lacroix or Canson was recommended) was placed on a silvered copper plate which was heated. White wax was melted on the paper. Excess wax was then removed by placing the waxed paper between blotting paper.

Salting the paper

The salting solution comprised, potassium iodide, potassium cyanide and potassium fluoride added to rice water containing sugar of milk. The waxed paper was placed in the salting solution and then dried. In this state it could be kept for some time.

Sensitising

The salted paper was floated on a solution containing silver nitrate and acetic acid.

Exposure

Generally exposure times were longer than with the ordinary calotype process.

Development

The negative was developed in gallic acid. This step could take an hour or so.

Fixing

Sodium hyposulphite was used as the fixing solution.

Direct Positives

Hippolyte Bayard, an independent inventor of photography, introduced a process in early 1839 that produced direct positive prints. Silver chloride paper was blackened by exposure to light, then immersed in a solution of potassium iodide and while still moist placed in the camera. The highlights of the image were bleached by the action of light. Similar processes were proposed by Vérignon, Lassaigne and Dr. Fyfe. A more complicated direct positive processes was also proposed by Dr. Schafhäutl.¹³

Minor Processes

Chromatype

This was announced by Robert Hunt in 1843. Copper sulphate and potassium bichromate were coated on paper and exposed to light. The image at first appeared as a dull brown negative, if exposure was prolonged a yellow positive image on a white background appeared. The exposed print was developed in silver nitrate producing a generally red image which was then washed in water to fix. Slight changes to the manipulation or the chemicals used gave different results, washing in common salt would remove the positive image which could be restored by exposing to light. Robert Bingham proposed the use of nickel sulphate in place of copper sulphate. The process was suitable for copying natural objects but no practical use was made of it.¹⁴

References & Notes