Morning work in afternoon thermal bath

Relaxing in Gallery

sea/son ... the SEASON

,,, thousands of projects in many contexts,

In these Easter cleaning between books magazines and papers photographs would

deepen a technique photography much used but little known ...

" Silver gelatin DOP "

Silver gelatin DOP is based on the light sensitivity of silver halides, which are suspended in a gelatin binder on a baryta paper support. DOPs made their first appearance in the mid 1880s and became the dominate printing process of the twentieth century. Due to the complexity of the process, silver gelatin papers have always been a manufactured product. As chemists’ understanding of silver halide chemistry increased over time, papers could be manufactured with a variety of characteristics, including varying light sensitivities, speeds, and tonal ranges. Papers were also produced with a variety of surface sheens, textures, paper thickness and paper tints. Optical brightening agents were introduced to papers beginning in the 1960s, which serve to make the highlights brighter providing papers with more contrast.

"Silver gelatin DOPs have a paper support. Most prints made before 1970 have fiber-based paper supports of varying paper weights. The standard weights are described by manufacturers in different ways including: heavy, medium, and light weight; single-weight, double weight, lightweight, extra thin. Water-resistant papers coated with cellulose acetate were made before the late 1960s. These papers were used in photo booths, as ID pictures, and for printing map reproductions, among other things that required fast processing. In the late 1960s papers coated with polyethylene, called resin-coated (RC) papers, were introduced. RC papers are coated on the back with clear polyethylene and on the front, directly below the emulsion, with pigmented polyethylene and are easily identified by their smooth plastic back. Specialty metallic papers were marketed until the 1970s. These have a special surface that give the print a metallic appearance". 

Significant advancements were made throughout the twentieth century to silver gelatin emulsion making for both negative and print materials. During manufacturing of the emulsion, silver nitrate is combined with a halide (usually a combination of bromide and chloride, though silver iodide papers were also made) in the presence of gelatin with an excess of halide present. The gelatin slows the formation of the crystals allowing for smaller, more uniform crystals to form and react with impurities (sulfur) in the gelatin, all of which make the silver halide crystals more light sensitive. The emulsion is then heated in a process called Ostwald Ripening which increases silver halide sensitivity and creates more uniform silver halide crystals. The next step is to remove impurities from the gelatin. Initially emulsions were shredded into noodles, washed to remove impurities, and then heated and re-melted. Later emulsion making required a complicated procedure of flocculation which required altering the pH of the emulsion causing the silver halides to precipitate out. The silver halides were washed and dispersed back into the emulsion. Another way of extracting impurities is through reverse osmosis through a thin membrane. Finally additional sensitizing chemicals and other additives are added. Gelatin is the perfect binder for silver halide crystals; it has the ability to swell allowing the penetration of processing solutions, but is tough and resistant to abrasions when dry. The gelatin emulsion was then machine coated onto a baryta paper support.

 A final thin layer of hardened gelatin was applied to act as a protective layer called an overcoat, also called a supercoat or topcoat.

DOPs can be contact printed or printed by enlargement through a negative. During exposure, a latent image is formed where light strikes the paper. Development reduces the silver ions in the latent image to visible silver particles in an oxidation-reduction reaction. Development is followed by a stop bath, which halts development and keeps the following fixing bath from being contaminated with developing solution. Next, unexposed silver halides are removed in a fixing solution, usually sodium thiosulfate, which dissolves silver halide crystals into a water soluble compound. Finally the print is washed thoroughly to remove residual processing chemicals and by products produced during fixing.

Photographers may choose to tone prints to alter the image color and/or to increase the stability of the print. Popular toners include gold, polysulfides, and selenium or a combination of sulfide and selenium.  Gold toning replaces part of the silver image with a more noble metal (gold). Gold toning usually produces a cooler neutral image tone of blue-black. Selenium and sulfide toners create a compound with silver that is more stable than silver alone. Image tones generally range from sepia, brown, purple, and purple-brown. This can be done by indirect toning in which after fixing the silver image is bleached and then immersed in the toning solution. The sulfide solution reacts with the silver halides to form silver sulfide. Direct toning does not require bleaching. Dye toning converts the silver image to a dye mordant that attracts dye from a dye solution. Finally, metal ferricyanide toning converts the silver image into silver ferricyanide complex which is then converted to a ferricyanide salt of a different metal (iron, copper, uranium). Dye toning and metal ferricyanide toning can result in a diverse rainbow of image colors.

The Royal Photographic Society

Bath, UK, 9 December 2011 – The Royal Photographic Society has made a call for nominations for its prestigious annual Awards which honour individuals across all areas of photography. Nominations are sought for The Society’s Progress Medal and in categories ranging from ‘Outstanding Service to Photography’, to those honouring individuals in education, science and involved with The Society itself. Award winners will be announced at a special event to be be held in London on 6 September 2012. The Awards ceremony is sponsored by The Macallan, a global luxury brand which has developed a keen interest in promoting photography.

Full details of each Award and a nomination form can be found on The Society’s website: http://www.rps.org/annual-awards or may be had on request from Awards Manager Jo Macdonald by emailing: jo@rps.org. Nominations are required by 24 February 2012.

In addition to the Award winners the ceremony also brings together students that have been awarded educational bursaries by The Society during 2012 developing new and young talent and bringing them wider recognition from their peers.

The Society’s Director General Dr Michael Pritchard noted: “The Society’s Awards are unique in not being restricted to Society members and in their breadth. They honour men and women internationally who have made a significant contribution to a particular aspect of photography – across the art and science of photography or in important areas such as photographic education, publication and curatorship. I would encourage nominations”.

The Society has made Awards to photographers and those in photography since 1878 when its Progress medal was first awarded. There are now fifteen categories. In addition The Society also awards Honorary Fellowships of The Society – an honour it first betsowed in 1895. Recent Award winners have included photographers Terry O’Neil, Albert Watson, Annie Liebovitz and Martin Parr, and individuals Philippe Garner, Sir David Attenborough and Tim Berners-Lee, alongside scientists and museum and gallery curators

Bridge spring

gold bath

Early in the history of photography conservation, cracks were a tool to identify albumen photographs.

Exposure to Moisture Causes Changes in Albumen Prints

The process is as follows : Sensitise the paper as usual on a nitrate of silver bath, at 20 per cent., and print in the ordinary way; only, it is better to overprint it a little. Then place the proof in a dish of water in order to free it from the greater part of its nitrate; put it, afterwards, in a dish of salted water, and leave it there from five to ten minutes. The object of this bath is, to convert every trace of free nitrate that might have been left in it by the first bath into chloride. This bath is essential to prevent the decomposition of the following bath, in which the proof is to be next placed. This bath is composed as follows :

Sesquichloride of gold
15 grains.

Phosphate of soda (the purified tribasic phosphate of commerce)
300 grains.

Distilled water
1¾ pints.


N.B. This bath ought to be completely neutral, or, at all events, rather alkaline than acid. If it should be acid, it is a sign that the chloride of gold was not properly prepared.

As soon as placed in this bath, the tone of the proof begins to change, and passes rapidly from red to purple, violet, and black; at the same time, the solarised parts of the proof lose their dead tone, and all their details are developed in an astonishing manner.

The colouring may be arrested at any moment. If it be stopped at the purple tone, the proof will appear sepia after the operation, if stopped at the black tone, it is rather black or grey. After this bath, the proof is put in a new hyposulphite of soda bath, of 20 per cent., in which -a little Spanish white has been put in suspension, and finished as usual.

These proofs are so stable that they resist the action of a cyanide of potassium bath for a very long time.

The great advantages of this process are:
1. The colouring bath is perfectly neutral, and cannot produce any decomposition in the hyposulphite of soda; 2. The colour is entirely produced by the gold, which has hitherto been considered the most certain means of colouring, since the proof is not in contact with the hyposulphite until after it has received its colour. Finally, there does not exist in the bath any organic acid to determine its spontaneous decomposition, and the precipitation of the gold in a metallic state.

The colouring bath described above may be prepared beforehand, it does not decompose by keeping if care be taken that none of that used is returned to the bottle. It is likewise very economical, since with 15 grains of chloride of gold, sixty or seventy pictures, 24 X 30, may be coloured. In order to make sure that no traces of gold that may be left in the bath after use shall be lost, the remains of these baths should be poured into a bottle containing some bits of copper.




my BATH