COLLODION PROCESS

The 'collodion process' is an early photographic process which gave way in the late 19th century to today's gelatin emulsion process. It was invented in the same time by Frederick Scott Archer and Gustave Le Gray about 1850, and developed further by others.

Contents

The original idea

History

The basic method

The collodion process becomes widely adopted

Details of the method

The reaction caused by collodion process

References

The original idea

In 1851, Frederick Scott Archer introduced the wet plate process, also called the collodion process after the carrier material used. It was the first widely used image to negative process and together with the invention of albumen paper they made a unbeatable team for many decades. Even after the discovery of the dry plate by Dr. Richard Maddox, about 20 years later, its popularity did not wane among professional photographers and some practiced this art until the 1970s to make portraits and id card photos. The definite advantage was that the collodion plate had a depth of detail and sharpness unprecedented. Other benefts to the collodion process was that a paper print cost about one-tenth the cost of a daguerreotype image. The collodion process was never patented, which allowed anyone to use the process, which kept the process alive for a long time. A few photographers still use the process for art photography.
This process was also known as the wet plate process because the plate had to be used before the photographic emulsion dried.
There have been some attempts, most notably by Joseph Sidebotham, Richard Kennett and Frederick Charles Luther Wratten to ''dry'' the collodion process but they lacked permanent success because, while giving the plates a longer shelf life, they did not really improve photography but introduced a major drawback: The photographer could not make the plates himself but had to buy them. Due to the arduous traveling conditions and long ways the collodion dry plate mostly caught on locally.
Variations of the collodion process are :

★ The ferrotype or tintype

★ The ambrotype
In 1864 W. B. Bolton and B. J. Sayce published the germ of a process which revolutionized photographic manipulations. In the ordinary collodion process of Scott Archer, a sensitive film is procured by coating a glass plate with collodion containing the iodide and bromide of some soluble salt, and then, when set, immersing it in a solution of silver nitrate in order to form silver iodide and silver bromide in the emulsion.
The question that presented itself to Bolton and Sayce was whether it might not be possible to get the sensitive salts of silver formed in the collodion whilst liquid, and a sensitive film given to a plate by merely letting this collodion, containing the salts in suspension, flow over the glass plate. Gaudin had attempted to do this with silver chloride, and later G. W. Simpson had succeeded in perfecting a printing process with collodion containing silver chloride, citric acid and silver nitrate; but the chloride until recently has been considered a slow working salt, and nearly incapable of development.
Up to the time of W. B. Bolton and B. J. Sayce's experiments silver iodide had been considered the staple of a sensitive film on which to take negatives; and though bromide had been used by Major Russell and others, it had not met with so much favour as to lead to the omission of the iodide. At the date mentioned the suspension of silver iodide in collodion was not thought practicable, and the inventors of the process turned their attention to silver bromide, which they found could be secured in such a fine state of division that it remained suspended for a considerable time in collodion, and even when precipitated could be resuspended by simple agitation.

History

At the time, a glass plate was used with albumen (egg white) as a binder for the silver nitrate. The two major drawbacks of albumen were that it had a very long exposure time and the process itself was very complicated. By substituting collodion for albumen, the exposure time was reduced drastically and the process became simpler.
The glass plate itself allowed for easy duplication, but the collodion made the image sharper as well as reduced exposure time. This became crucial in history as collodion allowed for growth in commercial photography. Studios would use this method for porcelain prints, fabric, paper, jewelry, photosculpture, as well as carte-de-viste.

The basic method

The outline of the method was to dissolve a soluble bromide in plain collodion, and add to it drop by drop an alcoholic solution of silver nitrate, the latter being in excess or defect, according to the will of the operator. To prepare a sensitive surface the collodion containing the emulsified sensitive salt was poured over a glass plate, allowed to set, and washed till all the soluble salts resulting from the double decomposition of the soluble bromide and the silver nitrate, together with the unaltered soluble bromide or silver nitrate, were removed, when the film was exposed wet, or allowed to dry and then exposed.
The rapidity of these plates was not in any way remarkable, but the process had the great advantage of doing away with the sensitizing nitrate of silver bath, and thus avoiding a tiresome operation. The plates were developed by the alkaline method, and gave images which, if not primarily dense enough, could be intensified by the application of pyrogallic acid and silver nitrate’ as in the wet collodion process. Such was the crude germ of a method which was destined to effect a complete change in the aspect of photographic negative taking; but for some time it lay dormant. In fact there was at first much to discourage trial of it, since the plates often became veiled on development.

The collodion process becomes widely adopted

M. Carey Lea of Philadelphia, and W. Cooper, jr., of Reading, may be said to have given the real impetus to the method. Carey Lea, by introducing an acid into the emulsion, established a practicable collodion emulsion process, which was rapid and at the same time gave negative pictures free from veil. To secure the rapidity Carey Lea employed a fair excess of silver nitrate, and Colonel H. Stuart Wortley gained further rapidity by a still greater increase of it; the free use of acid was the only means by which this could be effected without hopelessly spoiling the emulsion.
The addition of the mineral acids such as Carey Lea employed is to prevent the formation of (or to destroy when formed) any silver sub-bromide or oxide, either of which acts as a nucleus on which development can take place. Abney first showed the theoretical effect of acids on the stib-bromide, as also the effect of oxidizing agents on both the above compounds (see below). A more valuable modification was introduced in 1874 by W. B. Bolton, one of the originators of the process, who allowed the ether and the alcohol of the collodion to evaporate, and then washed away all the soluble salts from the gelatinous mass formed of pyroxylin and sensitive salt.
After washing for a considerable time, the pellicle was dried naturally or washed with alcohol, and then the pyroxylin redissolved in ether and alcohol, leaving an emulsion of silver bromide, silver chloride or silver iodide, or mixtures of all suspended in collodion. In this state the plate could be coated and dried at once for exposure. Sometimes, in fact generally, preservatives were used, as in the case of dry plates with the bath, in order to prevent the atmosphere from rendering the surface of the film spotty or insensitive on development. This modification had the great advantage of allowing a large quantity of sensitive salt to be prepared of precisely the same value as to rapidity of action and quality of film.
A great advance in the use of the collodion. bromide process was made by Colonel Stuart Wortley, who in June 1873 made known the powerful nature of a strongly alkaline developer as opposed to the weak one which up to that time had usually been employed for a collodion emulsion plate, or indeed for any dry plate.

Details of the method

An example of the preparation of a collodion emulsion and the developer is the following: 2 3/4 fl oz of alcohol, 5 fl oz of ether, 75 grains of pyroxylin. In 1 fl oz of alcohol are dissolved 200 grains of zinc bromide 2; it is then acidulated with 4 or 5 drops of nitric acid, and added to half the above collodion. In 2 fluid drachms of water are dissolved 330 grains of silver nitrate, 1 fl oz of alcohol being added. The silvered alcohol is next poured into the other half of the collodion and the brominized collodion dropped in, care being taken to shake between the operations.
In metric units: 110 ml of alcohol, 200 ml of ether, 7 g of pyroxylin. In 40 ml of alcohol are dissolved 18 g of zinc bromide 2; it is then acidulated with 6 to 8 drops of nitric acid, and added to half the above collodion. In 10 ml of water are dissolved 30 g of silver nitrate, 40 ml of alcohol being added. The silvered alcohol is next poured into the other half of the collodion and the brominized collodion dropped in, care being taken to shake between the operations.
An emulsion of silver bromide is formed in suspension; and it is in every case left for 10 to 20 h to what is technically called "ripen," or, in other words, to become creamy when poured out upon a glass plate. When the emulsion has ripened it may be used at once or be poured out into a flat dish and the solvents allowed to evaporate till the pyroxylin becomes gelatinous. In this state it is washed in water till all the soluble salts are carried away. After this it may be either spread out on a cloth and dried or treated with two or three doses of alcohol, and then redissolved in equal parts of alcohol (specific gravity, 0.805) and ether (specific gravity, 0.720). In this condition it is a washed emulsion, and a glass plate can be coated with it and the film dried, or it may be washed and some of the many preservatives, such as albumen, beer, coffee, gum, etc., applied.
The type of a useful alkaline developer for collodion plates is as follows:
I. Pyrogallic acid - . - ' 96 g
Alcohol 1 oz.
2. S Potassium bromide - . . 12 g
Water distilled 1 oz.
Ammonium carbonate - . 80 g
Water 1 oz.
To develop the plate 6 minims of No. 1, 3/4 drachm of No. 2, and 3 drachms of No. 3 are mixed together and made to flow over the plate after washing the preservative off under the tap. Sometimes the development is conducted in a flat dish, sometimes the solution is poured on the plate.i The unreduced salts are eliminated by either cyanide of potassium or sodium hyposulphite. Intensity may be given to the image, if requisite, either before or after 'the "fixing" operation. Where resort is had to ferrous oxalate development, the developer is made in one of two ways—(1) by saturating a saturated solution of neutral potassium oxalate with ferrous oxalate, and adding an equal volume of a solution (10 grains to 1 oz. of water) of potassium bromide to restrain the action, or (2) by mixing, according to Eder's plan, 3 volumes by measure of a saturated solution of the potassium oxalate with 1 volume by measure of a saturated solution of ferrous sulphate, and adding to the ferrous oxalate solution thus obtained an equal bulk of the above solution of potassium bromide. The development is conducted in precisely the same manner as indicated above, and the image is fixed by one of the same agents.

The reaction caused by collodion process

The reaction of collodion and silver nitrate produce silver iodide. Silver iodide is unstable when exposed to light leaving silver. The silver is oxidised by ferrous sulfate turning black. The rest of the silver iodide is reduced by hypo or cyanide. Most of the silver tends to end up in the stabiliser bath.

References

★ Contemporary Wet Plate Photographs and Video

★ See work by the Masters of Collodion; Revival of Wet-Plate Collodion Process

★ Modern images of the ambrotype process. Tutorials also.

★ AlternativePhotography — Wetplate collodion process

★ History of photography from 1839 to 1879

★ Meier, Alf B. ''Basic Photography - a manual for the training of fashion photographers, (Frankfurt/M.: Jentzen oHG, 1992)''

★ An account of Sayce's process is to be found in the Photographic News of October 1865, or the Photographic Journal of the same date.

★ The advantages of this salt were pointed out by Leon Warnerke in 1875.

★ Modern ambrotype images and an overview on the wet-plate collodion process

★ A brief history of the wet collodion process

★ How the wet plate collodion process works