The English scientist and astronomer Sir John Herschel discovered this process in 1842. He considered it mainly as a means of reproducing notes and diagrams. It was Anna Atkins who brought the process to photography. In 1843 she created a limited series of cyanotype books that documented ferns and other plant life from her extensive pressed plant collection. Atkins placed specimens directly onto coated paper, allowing the action of light to create a silhouette effect.

To produce a cyanotype, equal volumes of solutions of different iron salts are mixed. This photosensitive solution is then applied to a watercolour paper (or another support such as fabric or glass). The paper is dried in a dark place.

A positive image is produced by exposing the coated paper to ultraviolet light through a contact negative. The sun may be used but a UV box gives more accurate results. The reaction between the ultra-violet light and the photosensitive emulsion results in an insoluble blue image.

After exposure developing of the image involves the residual chemicals being rinsed off with running water leaving the characteristic blue cyanotype image.

Cyanotypes may be toned intensifying the blue by introducing chemicals that change the iron in the printed image. There are a variety of reagents that can be used in toning, including tannic acid, tea, wine, pyrogallic acid or even cat urine.


This process is named after the brown pigment favoured by Flemish painter Van Dyck.

The Van Dyke Brown process was devised by W J Nichol in 1899, based on early experiments of the Kallitype process of Sir John Herschel in the 1840s.

To produce a Van Dyke Brown separate solutions of ferric ammonium citrate, silver nitrate and tartaric acid are prepared and then mixed together in equal parts to produce a light sensitive emulsion. The emulsion is painted onto watercolour paper and allowed to dry. A negative, the size of the final print, is prepared. The negative is exposed, under ultra-violet light, against the coated paper to produce a contact print. The contact print is washed, toned (if desired), fixed, cleaned and washed a final time to produce the finished print.

The reaction between the ultra-violet light and the photosensitive emulsion results in an insoluble, reddish brown characteristic Van Dyke Brown image.


In 1839, Mungo Ponton discovered that dichromates are light sensitive and in 1852 William Henry Fox Talbot found that colloids such as gelatin and gum arabic became insoluble in water after exposure to light. In 1858, John Pouncy used those discoveries adding coloured pigment with gum arabic and dichromate to create the first colour photographic images.

Gums may be produced from a single negative but it is more common to separate images into CMYK (cyan, magenta, yellow and black) negatives so that a multi coloured image can be built up.

Images are produced by overlaying multiple layers of differently coloured pigment. Each layer of pigment comprises of a mix of two solutions, a watercolour pigment suspended in gum arabic and a separate solution of potassium dichromate. When the two solutions are mixed a tinted, photosensitive emulsion is produced. Each pigment layer is individually coated, registered, exposed with a different separation negative and washed. It is not uncommon for a full colour gum image to comprise of up to 7-12 individual pigment layers.

The image is produced by exposing the coated, heavy weight watercolour paper to a source of ultraviolet light through a contact negative. The negative is sandwiched between the prepared paper and a sheet of glass and the negative must be in registration with previous exposures. To develop, a print is then floated face down in a bath of water to allow excess dichromate and pigmented gum to wash away. Several changes of water bath are necessary to clear the print. Afterwards, the print is hung to dry. This is repeated for each pigment layer. When all layers are complete and dry, a clearing bath is used to extract any remaining dichromate.

As gum prints tend to be multi-layered images they are sometimes combined with other alternative process printing methods such as cyanotype and platinotype. Further by using different pigments with different negatives the possibilities are endless.
As gums are built up from multiple layers of pigment it can take days to produce a single print.


Many early photographers experimented with etching photographic images onto metal plates including Fox Talbot in the 1850’s.

Photopolymer plate, sometimes known as solar plate, is an offshoot of flexography printing and was first used for art print making by Dan Welden in 1987 when experimenting with non toxic etching processes.

A thin steel plate is coated with a layer of ultra-violet (UV) sensitive polymer. The plates are used by artists or photographers who wish to etch an image into the plate and then print the image using an etching press.

Anything copied, drawn or printed on to clear Mylar or acetate can be exposed onto a photopolymer plate including film positives output from a camera or digital photographs printed on transparent film.

The film is then overlaid on the plate and exposed to UV light. Wherever the UV light hits the plate the UV sensitive polymer is hardened whilst other parts of the polymer blocked from the UV light by darker parts of the transparency remain soluble. The plate is developed by scrubbing it gently in water to wash away the remaining soluble residue. This leaves a plate that is etched with lines and grooves that make up the image.

Plates may be etched in the sun although photographic images are more successfully etched under a UV light source, often under vacuum.

The plate can then be inked and the image printed on art paper using an etching press either in intaglio or relief, in single or multiple colours.
As with traditional etched prints, photopolymer prints may be hand coloured, inked “a la poupee” or used with “chine colle” – coloured rice paper.


The daguerreotype was the most popular photographic process until the 1850’s. Images could only be produced on highly polished metal plates and each image was unique.

Salt prints were the very first stable, positive, reproducible silver based photographs produced. The process was discovered by William Henry Fox Talbot in 1834. This was the culmination of many years, by many clever amateur scientists, experimenting with light sensitive silver salts.

A salt print is produced by coating 100% cotton watercolour paper with a salt solution. Dried and then coated with a silver nitrate mixture. The paper is exposed with a dense negative under UV light up to 20 minutes or more. The paper is then moved through a series of washing baths, toned, fixed and cleared. Ten baths is typical and it may take an hour to develop each print.

There are variations in salt print making but all are very time consuming. Moreover there are no short cuts and the final print is influenced by:

• the paper
• the various formulae of chemicals and additives for coating
• humidity
• the quality of the negative
• the UV source
• toning
• washing and fixing.

The resulting images have a wider tonal range than other traditional printing processes and the effort required is well rewarded.


Platinum and Palladium printing like most alternative processes evolved over time thanks to the efforts of scientists, physicists and artists.

From the very early 19thC, several German chemists, followed by English scientists and artists, were looking at the effects of platinum chlorides exposed to UV light. Not until the 1870s did a reliable paper, coated with platinum, become a commercial reality. After World War I, platinum became scarce and expensive, so palladium (a similar salt to platinum) was used by photographers for fine art printing. Commercially produced coated papers were discontinued around the late 1930s. Today, both platinum and palladium remain relatively expensive materials compared to silver halides.

Prints are made using an enlarged negative the same size as the desired print. A solution of palladium, platinum and a sensitizer is coated on to high quality watercolour paper. The negative is placed on the coated paper then exposed to UV light. Subsequently, the print goes through a sequence of developing and clearing agents before washing and drying.

Platinum/palladium prints are considered to have the greatest tonal range of any monochrome printing process, partly due to the salts being laid down on the surface of the paper, and not embedded in the gelatin as in silver prints. In addition, both platinum and palladium prints when correctly processed are extremely stable and will not deteriorate.

For many photographers and collectors, platinum/palladium prints have a “presence”.


The bromoil process can be defined as turning a silver image into an ink image.

Bromoil printing is based on the earlier 19thC oil print experiments, and reached its peak during the first half of the 20thC, when photographers were looking for a softer, romantic style in their photography. Edward Steichen, Robert Demarchy, and Harold Cazneaux were among many practitioners of this art form which became part of the ‘pictorialist’ movement.

The process consists of 3 stages:

• exposing a negative image on to silver gelatin paper;
• removing the silver by bleaching, hardening and ‘fixing’ the latent image;
• applying greasy lithographic ink.

The technique relies on two factors:

• the effect of the gelatin in the photographic paper receiving differential amounts of light through the negative: where the negative areas are transparent (shadows in the print) the gelatin receives more light and is subsequently hardened more than the highlight areas of the print.

• the oil and water effect: prior to inking the hardened gelatin photographic paper is briefly soaked. Highlight areas less affected by hardener will absorb moisture and repel the greasy ink but the ink is taken up in the hardened and dryer shadow areas.

You may wonder why anyone would want to turn a perfectly good silver image into a bromoil. Silver will deteriorate in time, but an ink image will last as long as the paper. More importantly there are many opportunities to manipulate the print during inking so it becomes a personal and creative work, revealing the hand of the artist.


The Argyrotype process is a slight exception to the historical processes mentioned elsewhere. Whilst it has its roots in the work of Sir John Herschel and his Argentotype iron-silver process, Mike Ware developed it in the 1990s. Silver sulphamate takes the place of the usual silvers used with the advantage of increased stability and light fastness. The resulting images can be toned as per other silver based processes with for example selenium or gold. Similar to the cyanotype process, the sensitizer solution is brushed onto paper, sandwiched with a negative and exposed under UV light. As silver is involved it is necessary to ‘fix’ the image with sodium thiosulphate to remove any insoluble silver salts that would degrade the image over time. As with all such processes, a long bath in water is required to clear the image of unwanted chemicals.


Lith prints have many moods – soft and dreamy to hard and gritty. The cold gritty effects are particularly suited to the imagery of harsh industrial sites. On the other hand, warm, soft and dreamy landscapes are possible including coloured ones.

This versatility is due to many factors – paper, developer type temperature and dilution, length of development and…serendipity.

Using a normal negative, black and white photographic paper is overexposed (2-3 stops) and underdeveloped in very dilute lith developer. The broad result is a print with black shadows, coloured mid-tones and white highlights. Colour ranges from peach to olive shades and deep cold browns.

A particular mode of action of high energy lith developers is known as “infectious development”. As dark tones appear and development continues, the darker they become and the faster development spreads in the print. The printer must then decide when to “snatch” the print and stop further development.

For all its variables, lith printing is well suited to matching the subject matter with the desired “look” in the print.

English photographer Tim Rudman has produced beautiful and varied lith prints, as well as teaching lith printing through classes and his excellent books.