PhotoHistory

From: PHOTOGRAPHY OF TO-DAY

By H Chapman Jones, 1913

THE USE OF GELATINE

(NOTE: all of the old sources seem to prefer the spelling gelatine over the modern version without the terminal ‘e’ — we have retained that spelling, while modernizing most other words.)

We have seen how the various operations in the preparation of sensitive plates suitable for getting negatives on, were gradually transferred from the individual plates to the bulk of material with which the glass was to be coated. Each step in this direction gets nearer to the possibility of making plates on the large scale commercially and so saving the photographer himself, not only from a great deal of trouble, but also from much anxious thought at the very time when his attention is needed for other matters. Another advantage of the production on a large scale is uniformity and therefore reliability, for each individual plate is no longer a separately made article with all possibilities of failure on its own account, but it is one of many all as alike as they can be made, and if a few of a large batch prove satisfactory, the probability is that the remainder are equally good.

About the time that we are now considering, a few years before and after 1870, the dried collodion emulsion was an article of commerce and dry collodion emulsion plates were also prepared commercially, though on what would now be considered as an exceedingly small scale. Dry collodion plates can still be purchased, or at least they were on the market a very short time ago, but their use is restricted almost entirely to the preparation of lantern slides.

On the part of photographers as a body, there was for long after this time a distinctly adverse disposition with regard to commercially made plates and other sensitive material. There was a kind of feeling that a photographer ought to prepare his own plates, and that he was hardly fit to associate as a photographer with other photographers unless he did so. It took quite a long time for the very real advantage in the use of a commercially made article to be appreciated. It is difficult to understand this conservative attitude at the present time, when besides the advantages already mentioned, the gain in the quality of the materials is so obvious when a staff of workers can devote their whole attention to the making of them, and the large output renders it profitable to adopt elaborate precautions that would have been quite impossible with the man who made only the few plates that he required for his own use. But it must be remembered that the perfection of the processes for the commercial preparation of sensitive material was very gradual, and the methods at first employed did not differ from those adopted by the individual photographer, and it is possible that the man preparing plates for his own use tended to be a little more careful than he who prepared them for sale. This possibility is not a matter of photography but of human nature, for however honest and generous one may be, most of us are willing to take a little more trouble for ourselves than for other people. But the advantages of manufacture on the large scale gradually became so obvious that since some twenty years or so ago a photographer would no more think of making his own plates than of making his own cameras and lenses.

Except for a few special purposes generally in connection with trade work, collodion is now altogether supplanted by gelatine as the medium in which the sensitive salt is held. It was collodion that popularized photography, so that every one considered it his duty to have his portrait taken from time to time and give copies to his friends, and tourists were not satisfied unless they brought home photographs of the objects of interest associated with the places that they visited. But it was gelatine that carried the development a stage further, and convinced millions of people how easy it would be to make their own photographs. This led to the production of a type of amateur photographer quite different from the original, who thought no trouble too great and no process too messy, so long as he succeeded. The new type knew nothing whatever about photography and cared nothing about it, he merely, as the Kodak Company expressed it, “pressed the button,” and all the photographic work was carried out for him by a trade firm. Between these two extremes there is now represented every degree of interest and enthusiasm.

But the introduction of gelatine was like almost all other improvements in photographic work, very gradual. It was not so much that gelatine as a medium was a novelty, but rather what could be done with it. As collodion took years to supplant the Daguerreotype process, so gelatine took many years to oust collodion. Even when the superiority of a new method is demonstrated, the actual workers who have become skilled in the older method, are not very ready to change their habits and learn a new process.

It was in 1871 that Dr. R. L. Maddox published a formula for preparing a gelatine emulsion of silver bromide. It was a very imperfect process and hardly comparable with the gelatino-bromide process of to-day. Others were at work with gelatine and sought to make the use of it a commercial success, but they treated it, as was natural, after the manner of collodion, and sought to sell the emulsion or the dried emulsion — the pellicle; it was not yet that dry gelatine plates ready for use were offered for sale. The greater sensitiveness of some of these newer preparations, when compared with collodion plates, proved a disadvantage rather than otherwise, as it caused many who tried them to fail on account of the disastrously long exposures that they gave.

Various improvements were effected in the use of gelatine, but the especial feature of the modern dry plate, that is its very great sensitiveness as compared with the plates prepared by any earlier process, dates from 1878. It was in this year that Mr. Charles Bennett, a member of the well-known firm of hatters and an amateur photographer of the early and enthusiastic type, exhibited some photographs taken with extraordinarily short exposures. His method was to keep the emulsion warm, or rather to prevent it getting quite cold (about 90 F.), for a few days, at longest about a week. Dry plates had been made and sold before this, for towards the end of 1877 they were advertised for sale by Mr. Kennett and also by Wratten and Wainwright, who supplied both collodio-bromide and gelatino-bromide dry plates. But at this time a well-known authority writes: “Probably the final test of the excellence of a dry plate process will consist in its fitness for commercial sale, ready prepared for use, with some certainty on the part of purchasers that reasonable excellence may be secured in the use of such plates. This is a test which, judging from the reports of the users of commercial dry plates, either no process, or no manipulation of any process, has yet stood satisfactorily.” A year later, that is after Bennett’s method of getting increased sensitiveness had been published, we find an experienced photographer who used both collodion and gelatine emulsions, always preferring collodion as being more easy and certain to work; which of course was natural, as the experience with collodion was considerable and gelatine was comparatively new. A noted photographer found Swan’s gelatine dry plates to require from a half to a sixth of the exposure of a wet collodion plate, while Wratten and Wainwright said that their gelatine dry plates needed only one-fifteenth of the exposure of a collodion plate, and in a poor light only one-fortieth.

Thus dry plates were gradually being improved, and in 1879 Mr. Joseph Paget offered a prize of 50 pounds sterling for the best dry plate process; the Paget Prize Plate Company was the result of this competition. Before the close of 1880 there were many makers of gelatino-bromide dry plates, the new industry had established itself, and it only remained to perfect it in details. It was soon found that a few minutes at the temperature of boiling water was as effective in getting greatly increased sensitiveness as a week at a temperature equal to that of a very hot summer’s day in England, and Dr. Monckhoven found that by adding ammonia to the emulsion the heating might be dispensed with altogether.

Although by this time, 1880, the modern gelatino-bromide dry plate was being prepared commercially by many firms, they were prepared in much the same way that an individual experimenter would make a dozen or two for his own use. But the possibility of buying plates which needed absolutely no preparation to fit them for use, plates that could be taken from their package and put straight into the camera, and that would keep in good condition for weeks if not months either before exposure or between exposure and development, soon began to cause a great addition to the number of those who practiced photography. The greatly increased sensitiveness of them as compared with collodion soon made them a necessity for the professional portrait photographer, for the possibility of getting a sufficient exposure in four seconds instead of forty or sixty, was too great an advantage both to the photographer and to his sitters to be neglected.

The demand for dry plates therefore gradually increased, and the need for machinery to take the place of hand work soon began to be felt. But there was no machinery available for cleaning glass plates and coating them with a warm gelatinous mixture. Of course inventors were soon at work, but only experience could decide as to the efficiency of the apparatus devised. In October, 1888, the manager of one of the largest plate-making companies wrote to the author: “Up to the present all (our plates) have been hand-coated for the simple reason that we have not seen any machine which worked to our entire satisfaction until quite lately. Such a machine is now completed for us and we hope to have it in work in about a month. It coats very perfectly, and has at least two very desirable qualities, namely, it puts a measured quantity of emulsion upon each plate and none whatever on the back.” Coating by hand means that the warm emulsion was poured from a teapot on to the plate held in the hand, caused to flow all over the plate by tipping it as required or by the use of a glass rod, that the plate was then put on a level stand until the emulsion had cooled and “set,” and then dried. A coating machine would coat more than a thousand large plates in an hour.

Gelatine plates at the present time are all made in factories built for the purpose. Every precaution is taken to avoid dust, for dust on the plates means specks in the negative and this means spots on the print. For this reason large towns are avoided, and all the air that enters those parts of the factory concerned is filtered. Some idea of the effect of the filtration may be obtained from the fact that at a factory away in the country, it was observed that some of the men engaged in changing the filtering cloths were always ill after the operation, which was done once in three months. As soon as the connection between the filter cloth changing and the illness was discovered, the men were provided with suitable respirators and then their health did not suffer.

This indicates a very considerable accumulation of pathogenic germs on the filters as well as all the dust and soot and obvious dirt. But even this is not sufficient precaution, and it is desirable to arrange so that there shall be no crevices or spaces that cannot be easily cleaned and that might therefore allow an accumulation of dust, and to wash the floor every morning. It will be understood that this indicates the general character of the precautions necessary, and that these will vary somewhat according to needs of different localities and the ideas of different managers.

Considerable difficulty was experienced at first in getting suitable glass. Plate glass would be much too costly, and sheet glass with a very uneven surface or with specks or other irregularities in it is obviously unsuitable. Good sheet glass being obtained, it is cut into pieces of the required size and any pieces that show flaws are rejected. The pieces of glass are then fed into a machine which carries them between moving brushes, over which a suitable cleaning liquid, such as a solution of carbonate of soda, is constantly flowing. They are carried through plain water to complete the washing, and then generally receive a coating of a dilute solution of gelatine containing chrome-alum, so that when it dries the plate is covered with a very thin film of insoluble gelatine. This substance enables the emulsion film to adhere more securely to the glass. Without it the film might swell up away from the glass in blisters, or “frill” at the edges, or when dry it might come away from the glass or be peel-able from it so readily as to be unsafe.

The prepared glasses are now fed into the coating machine, and are carried along on a continuous band under the trough that deposits upon them a liquid sheet of the warm gelatinous emulsion, and they are carried along continuously through a tunnel or the equivalent which is cooled by means of ice. The liquid emulsion here sets to a jelly, and it is desirable that it shall set as quickly as possible to prevent the solid particles of silver salt from settling down to the lower surface of the film. The plates are then stacked in racks and taken to the drying chambers where they are maintained at a warm temperature, which however is not warm enough to run any risk of melting the jelly. A current of filtered air passes between the plates and through the chambers until the coating is dry. The plates are then removed in their racks to be cut up, if the smaller sizes such as half-plate and under are required. Mechanical arrangements are employed as far as possible for this cutting, as it is done in the minimum of dark red light. The plates are then examined, and those that show defects are thrown out, and the remainder are packed for sale. All the operations from the coating with emulsion onwards are done in rooms lit with only a red light that is so feeble that any one going in from outside would probably be ten minutes or more before their eyes became sufficiently accustomed to the semi-darkness to enable them to see their way about.

The emulsion is prepared in large quantities and stored in jars. One of the methods of securing uniformity, is to make several batches as nearly as possible alike and to mix them, so that the general average may vary but little. Every ingredient has to be suitably pure, and as an amount of impurity that would be far too small for detection by any method of chemical analysis might interfere vitally with the quality of the emulsion, the suitability of each constituent is tested by making a small quantity of emulsion with it, using other ingredients of known quality, and testing a plate coated with the resulting preparation. This applies not only to the gelatine, which is liable to vary very much according to the method of its preparation and purification, but even to the nitrate of silver, which is a definite substance and being easily crystallizable is supposed to be easily purified.

The principles involved in the making of a gelatine emulsion are exceedingly simple, and the practice is almost as simple when the most suitable procedure has been established. A portion of the gelatine is dissolved in water with the requisite bromide of potassium and a little iodide of potassium, for this latter is found to give certain desirable qualities that the bromide alone is deficient in. The nitrate of silver is dissolved in water and added to it. The insoluble bromide and iodide of silver are produced as a fine powder which permeates the whole solution, and nitrate of potassium is produced from the other constituents of the compounds. It is desirable, or rather it is necessary, to get rid of the nitrate of potassium together with the excess of the bromide of potassium present, and this is accomplished by cooling the emulsion until it becomes a jelly and washing the jelly in repeated changes of water. The rest of the gelatine is then added and the whole melted up together. It is well at some stage of the operation to filter the emulsion, as some of the silver salt is likely to clot together and form large particles which would give an irregular granularity to the negative made on the plate. For getting the enhanced sensitiveness the emulsion is heated as necessary before the main quantity of gelatine is added to it, or ammonia is used instead of the heating, or a combination of the two methods may be employed. No maker publishes exactly the method that he adopts, and probably there are little differences in the various factories, but so far as the user of the plates is concerned these differences are not very great. Some makers put more silver salt into their emulsions than others, some put thicker films upon their plates, some use harder gelatines, and there are other differences referring to the gradation that they yield that will be subsequently considered. But the main difference to the ordinary user is in the sensitiveness, and this is not a difference as between one maker and another so much as between the various kinds of plate that each maker produces.

It might perhaps be thought that the greater the quantity of silver salt and the thicker the film the better the plate if the other qualities remain the same. But no such broad generalization is justifiable. It is not unusual for an operator to be exposing plates all day, or as long as the daylight lasts, and then to develop his plates before going home. Plates with thick films take longer to wash than those with thin films, and if therefore he gives the same time to both sorts, the thinner films will perhaps be well washed while the thicker films will be imperfectly washed and suffer afterwards on that account. But will not the image on the negative be better for a liberal supply of silver salt, it may be asked. Even this does not follow. Many portraits are taken, especially of ladies and children, in which the whole subject is very light and shows very little contrast. If there is only a small difference between the darkest and the brightest parts of the subject, whatever it is, then a similarly small difference is all that is needed in the negative and more than sufficient silver salt, of course allowing a good margin, would only be in the way. On the other hand, a brilliantly lit landscape with a dark foreground, or an interior of a building in which a part is well lit and a part in deep shadow, needs a richly coated plate to do it justice. Hence it is desirable to prepare plates of different kinds for different purposes, as is customary, and it is well, where there is any doubt, to select a plate with a generous coating and make due allowance for the extra time necessary for its successful treatment.

Thus we have traced the very commencement of the dry plate industry and to a certain extent its development. As the practice of photography has become increasingly popular and the applications of it have increased, the demand for gelatine-bromide dry plates has grown enormously. The number and the size of the factories have increased, and the author has been assured by one who is well qualified to know that the number of plates coated every day would now have to be counted in millions. There does not appear to be any method of getting exact figures, but certainly it is remarkable that an industry only thirty years old should have grown at such a rate as it has and is still continuing to grow.

With the introduction of systematized labor and machinery, and doubtless also the competition between makers, the cost of photographic plates has gradually been reduced; and if there is added to this the fact that at each change the intrinsic value of the plates has been reduced, we get some remarkable figures by tracing the cost of photographic materials during the last seventy years.

The price of plates has always been very nearly proportional to their size; it is sufficient therefore to consider only one size in order to get a rough idea of the expenses attending the practice of the art in its various stages of development. The quarter-plate, 4 x 3 inches, dates back to the time of the Daguerreotype. One dozen silvered copper plates for this process cost thirty or thirty-two shillings if of the best quality, and inferior kinds were supplied down to as low a price as ten shillings. The amateur who was content with even this modest size must have found photography a costly pursuit when, instead of as we do paying a penny for a plate all ready for exposure in the camera, he had to pay half-a-crown for the plate, which he had himself to prepare by means of chemicals and special apparatus. But if he were content with paper negatives made by the calotype or Talbotype process or its modifications, the cost was really very moderate.

Expensive cameras then were unknown. Many were really nothing more than a box with the lens at one end and an arrangement for carrying the plate at the other, and the cost only a few shillings up to a pound or two. The various adjustments that we consider indispensable were only gradually introduced, and as in the Daguerreotype and wet collodion processes, only one plate could be dealt with at a time as it was prepared, only one plate carrier or “back” was necessary, and this for a single plate. The youth who made his own camera out of a cigar-box was really providing himself with the same type of instrument as was offered for sale at the photographic dealers. But this economy in the cost of the camera was pretty well balanced by the need for other apparatus, and the current expense was far greater than at the present time.

The glass plates used for the collodion process were about three shillings a dozen quarter-plate size. There were cheaper plates to be had and plenty of them were used, but there was a measure of risk in their want of flatness, uneven surface, and other defects. There was, however, a compensation for the high cost of glass plates, that if the negative was not satisfactory the plate could be cleaned and used again. At the present day it would cost more to clean and re-coat spoiled plates than to use new glass.

In 1847 hypo-sulphite of soda was cataloged at five shillings a pound. In 1853 it was two shillings, the next year eighteen-pence, and ten years afterwards five-pence. At the present time it can be obtained for less than two-pence a pound, or perhaps a little more if bought in small quantities.

We must not close our treatment of the present subject without a reference to the use of films instead of glass plates as the support of the sensitive layer in the production of negatives. The earliest negatives were made on and to a certain extent in the substance of paper. The irregularities of this material, as we have already pointed out, were constantly troubling those who used it, and the introduction of a separate substance to carry the sensitive compound that should be free from the structure of paper and under the photographer’s immediate control, first albumen and then collodion and finally gelatine, was a very important improvement.

As the substance of the negative, except the actual image, was required to be as transparent as possible, it was natural that glass should be used as the support for the sensitive film. A glass plate was not only the most transparent support possible, but, being rigid, it was easy to coat, easy to support in the camera, and every operation in the making of the negative and the getting of prints from it, was facilitated by its use. Being non-absorbent it could be easily cleaned and so freed from any impurities that would incur the risk of contaminating the sensitive material. At the present day glass still remains the best support so far as general manipulations are concerned, but it is heavy, bulky, and brittle, and in these details inferior to the paper used in earlier times. The advantages of paper were never forgotten.

A flexible film is so superior in portability to glass, that as early as 1854, that is in the first days of collodion and while the Daguerreotype process was still being worked, a roller slide was designed by A. Melhuish, that is an arrangement to slide into the back of the camera, and containing two rollers between which the sensitive film that is ready for exposure is stretched. By having a long band of film wound on one roller it can be transferred gradually to the other as needed for bringing a fresh portion into position for exposure. Thus a series of almost any number of exposures might be made without the need to use a dark room for changing the sensitive material. This method of working was popularized by the Eastman Kodak Company in 1885. In their cameras, the rollers are detachable bodily from the apparatus, the film as wound upon the roller by the makers is slipped into its place, and when it has been exposed, the receiving roller is turned several times so that a length of black paper attached to the end of the film shall be wound round it to protect it from the light, and is then removed for development, &c.

Many sorts of films were devised, some of them for working on rollers, others thick enough to stand alone like glass, others were arranged like drawing blocks, so that each as exposed might be stripped off leaving the next ready. Gelatine, collodion, varnish, and paper in various forms and combinations were used to make the films of. Some of the films were held on temporary supports such as paper, from which they had to be removed after exposure and development. Some had sensitive emulsion on both sides, so that any granularity due to the material of the film might not appear in the finished negative, as any unduly thin or transparent part would be neutralized by the light passing through it and giving a deposit, when developed, on the back film.

The roll-able film that is at present so largely used is of celluloid, which can be obtained free from structure and almost as transparent as glass. It is coated on one side with the sensitive emulsion, and to counteract the tendency to roll up or get curled when wet, a thin layer of gelatine is put upon the back surface. This kind of film was introduced in 1903 by the Kodak Company, and is in general use.