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times to give a soft contrast, for 5 times to give a medium or correct contrast, and for 8 times to give an exaggerated or hard contrast. The advantage of this plan of timing development is that the same contrasts can be secured at another time even if the temperature is different and if the developer has not the same activity as regards alkali.

I do not propose to make this paper a complete practical exposition of this factorial method of development, for I have recently published a handbook on the subject; and I will pass on to examine those variations in the character or proportions of the developer which in the past have been relied upon to secure control of results.

It may be noticed that I have spoken of the main course of development quite independently of the developing agent used. This is because I find that all developers, after all the tones have appeared, and leaving fog out of the question, do the same proportion of work on the different tones and attain the same result if the right time is allowed to each.

COMPARISON OF DEVELOPERS.

But in comparing the different developing agents, some (such as hydroquinone and strong pyro) will be found to give density in the upper tones quickly and to bring out detail in the lower tones slowly. Another class of developers, as metol or rodinal, bring out all detail very early in the total stages of development, while density in the upper tones seems to follow slowly. I show on the screen three exposed slips each of three gradations, developed in rodinal, 1 grain pyro, and 8 grains pyro respectively, and each taken out the moment the lowest tone had appeared. The rodinal has only attained a very feeble density in the upper tone, the 8 grain pyro a considerable density, and the 1 grain pyro an intermediate amount. After this commencement, all three strips would pass through exactly the same stages of contrast. I should leave in rodinal for 40 times appearance, in 1 grain pyro (no bromide) 18 times, and in 8 grain pyro (no bromide), 6 times appearance, in order to attain the same final result, and these figures (40, 18 and 6) would be the multiplying factors for these developers.

I also show strips developed in metol and hydroquinone respectively, one strip of each being taken out of the developer at 1, 2, 3, 4, 5, and 6 minutes respectively. It will be seen that metol is very much ahead in stage of development at 1, 2, and 3 minutes, at 5 minutes

hydroquinone has got level, and is identical. in all the tones, while at 6 minutes it is the denser of the two in all the tones.

The different types of developers have, therefore, different ways of going to work; but I have never been able to discover that the final result differs if each is carried to the same stage of development, and no bromide is used. I show strips developed by five different developers to illustrate this, each carried to the same steepness of gradation. Even with hydroquinone, which brings out detail last of any, I find (provided no bromide is used) that the faintest detail rendered by the exposure is fully brought out when development is carried far enough for a suitable contrast for printing on P.O.P. A developer exceedingly strong in pyro seems to have slight restraining effect, and holds back the lower tones in the early stages.

I have explained at greater length the differences between developers in the Photographic Journal, April, 1900.

I must, however, note that my experiments have not included ferrous oxalate developer, which has the reputation of giving a lower speed. It has, however, practically gone out of use for negative work, and is being abandoned even for testing purposes. There are also some indications that a few exceptional plates are a little more sensitive to a particular developer, but this variation seems scarcely sufficient to have any bearing on practical work.

INFLUENCE OF BROMIDE.

The restraining influence of a bromide in the developer has been explained by Hurter and Driffield in the Photographic Journal, July, 1898. They explain how its "holding back" influence on the lower tones is chiefly exercised in the early stages of development, and becomes less and less as development proceeds, until at an advanced stage of development the result with bromide is exactly the same in all gradations, as if the same plate were developed without bromide and carried to the same steepness of gradation. Even fog is only held back by bromide in the early stages of development. This explains many of the perplexing differences of experienceespecially as regards speed of plates-which have occurred between different experimenters. I show on the screen a series of slips illustrating this point.

The "holding back" power of bromide has in practice by far the greatest effect with deve

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densities of an exposed plate developed without bromide, and the lower illustration the same slip developed for the same time in the same developer with bromide added. It will be seen that the same steepness of gradation has been attained with both developers, but that the bromide has lessened the density in all the tones, and altogether prevented the lowest tone from appearing. With longer development, however, the lowest tone would come out, and the other tones increase in density to just the same extent as if no bromide were present. In these rough graphic diagrams, which are not intended to be exact, I have omitted the curves of under and over exposure.

The important part to remember is that this holding-back power is not exercised after the lowest tone has appeared; and it is therefore useless to add bromide some time after development has commenced. Most commercial plates of the present day develop sufficiently free from fog without the addition of a bromide, and I regard its use as quite unnecessary. Even in making lantern slides I have found that brilliant results can be secured without bromide in the developer.

WELL-BALANCED DEVELOPERS.

With each developing agent there is a strength which experience shows to have the most useful power without being in excess. This is usually from 2 to 4 grains to the ounce. There is also a proportion of alkali which gives sufficient energy without tendency to fog. This proportion with soda carbonate is about five or six times the weight of the developing agent. A developer thus proportioned is a well

balanced one. Changes in the amount of alkali alter the speed at which development proceeds but have no other effect on the gradations, except that an excessive amount is apt to cause fog.

OLD METHODS OF CONTROL.

I continue to see, that at Photographic Society demonstrations, beginners are advised to "feel their way" in development, to begin with a small proportion of alkali, and add more in course of development. Not the smallest power is conferred by the proceeding, for the stages of development follow exactly the same course as if a standard solution were used from the commencement.

Let me also consider the procedure which the maker's instructions and the text-books have advocated for dealing with over and under exposure with pyro soda developers, when unknown beforehand.

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It is usually advised that when the lower tones appear so slowly that under-exposure is feared, the developer should be diluted and more alkali added “to bring out detail." the other hand, if all the tones come out in such rapid succession that over-exposure is revealed, the traditional advice is to add more pyro at once-say, 2 grains to the ounceand an equal quantity of bromide, or else mix up and apply a new developer exceedingly strong in pyro and bromide. It is certain that such a developer has a great power of holding back the lower tones and altering gradation when it is used from the commencement. But I have never been able to discover that any such selective power exists when once these lower tones have appeared, or that the methods I indicate above, and which are usually termed tentative development, confer any power which cannot be equally well exercised by using a standard developer from the commencement.

The following are the details of a comparative trial which I show on the screen. A Paget XXXXX plate was exposed in a long series of gradations, and cut up into strips which were simultaneously developed in a two-grain pyro soda developer-no bromide, some in one dish, the remainder in another. The first tone appeared in 40 seconds, and as soon as all the tones were out (in 150 seconds) the following alterations were made, being previously got ready in measures. To the first set of strips (marked O for supposed over-exposure) two grains of pyro and two grains of bromide ounce were added. Το the second

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set of strips (marked U for supposed under-exposure) double the previous amount of alkali, and an equal bulk of water was added.

The strips were taken out of each dish at intervals, and afterwards compared to see if the gradations had been altered by these proceedings. There was no evidence of control by any such alteration other than that given in both cases by length of development. I compare one O and one U strip, both having attained about equal contrast. All the tones are also equal, a little fog being added in the case of U.

COMPENSATING FOR VARIED EXPOSURES.

It was Hurter and Driffield who proved that under and over exposures ought to receive the same time of development to secure the same contrast.

The strip of gradations on the screen, having alongside bits of over, medium, and underexposed negatives all developed for the same time, illustrates this. The over-exposed negative utilises the upper tones of the series, and is denser throughout. The under-exposed negative utilises the lower tones of the series and is thin throughout; but, except where they fringe on the extreme tones which are under or over the range of the plate, both negatives give prints of much the same detail and steepness of gradation. In this time development, therefore, the exposure decides the density of the negative.

I have often developed six negatives in a dish together-snapshots, interiors, and landscapes mixed; observed the time of appearance of the average high lights of the series (ignoring especially over-exposed high light, such as a window in an interior), and developed for the fixed multiple of this time, knowing that a similar amount of contrast would be secured in all the negatives. No doubt the use of an actinometer (my own exposure meter) in gauging the exposures helped towards the uniformity of result; but a very considerable variation of exposure is allowable, the over-exposures in such a series being dense, and the under-exposures thin.

When I have had rollable films to develop, I have also followed the same plan of timing, developing the whole roll at once.

In fact, it is with rollable films that the method of developing different exposures for the same time has come into general use. Probably nine-tenths of the rollable films developed in the last year or two have been developed without cutting up the roll at all,

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perhaps in most cases on account of ease and simplicity, without knowledge that it was the theoretically correct proceeding. I mention this because I notice that several photographers in speaking of the results attained by roll film developing machines seem to think it is a new thing to attain uniformity of results by developing the whole roll at once.

If known beforehand over-exposure can be compensated for by using a short factor developer with bromide. Under- exposure if known beforehand can not be improved; the use of more alkali or of a long factor developer such as rodinal does not bring out any more detail than the ordinary formula (no bromide) gives. The only hope lies in heated develop

ment.

SUMMARY OF PRINCIPLES.

Different developers vary in way of going to work, and speed of working, but not (bromide influence excepted) in final result.

Variation of the composition of a developer (bromide influence excepted) does not influence final result.

The bromide influence is not well under control, and cannot be exercised after all the tones have appeared. Bromide is best omitted from the developer, being unnecessary. The influence of time is quite sufficient for all control required.

THE TWO TIME METHODS.

There are two ways of deciding the time to develop, both depending on a previous trial. The first is my own factorial method in which the method makes correct allowance of most changes in the developer, for (usually) different kinds of plates or films and most important-for variations in temperature; it also allows for using the developer a second time. The second is the Hurter and Driffield methodlately followed in film developing machines-of developing for a fixed time with a fixed developer. With this plan it must not be forgotten that the time is only right for that particular plate or film, and for exactly one composition of developer used for the first time, and for one temperature. The variation for temperature can, no doubt, be given in a table, but if it is ignored-as one demonstrator seems to have advised-summer results will be very different from winter results. A second use of the developer, or its dilution, also requires an increase in the standard time.

MECHANICAL APPLIANCES.

In carrying out principles certain appliances are often helpful. With my factorial method, for instance, I devised a clock for the dark room with a ten minute dial and large minute divisions, as an ordinary watch, even a stopwatch, is not convenient. It is called the Eikronometer and has a calculator for giving the time to develop. It is a great convenience and its use has much increased lately. An ordinary metronome, or a half second chain pendulum, is a great help in counting seconds for the appearance of the image, either being better than a stop-watch. But I have always frankly explained that all the benefits of my factorial method can be obtained, although not so conveniently, with an ordinary watch. I, therefore, feel no hesitation in referring to a similar fact with regard to the two film-developing machines recently put on the market by two firms. They, no doubt, appeal to those who do not wish to use a dark room; but exactly the same results can be attained in a dark room by holding the whole roll of film in a U-shaped loop and see-sawing it, first through a bowl of water, and secondly through the developer in a basin for the standard time. These machines, of course, can only carry out the H and D time method, not my factorial plan. In developing films it is important not to stint the bulk of the developer. It is possible to use so small a quantity that its developing power is exhausted before the requisite work is done. In fact if negatives always contained the same proportions of high light and shadow it would be quite possible to control the steepness of gradation by limiting the total amount of developing salt.

DISCUSSION.

Mr. CHAPMAN JONES said he had learnt much from the paper, although a great part of it travelled over old ground. But when Mr. Watkins made a diagrammatic representation of what had taken place in development, he often failed to represent fairly what he had demonstrated by his experiments. One of the first diagrams indicated the course of development, and showed how a certain number of particles, after exposure by light were, during development, reduced in a certain proportion, and by further development in a further proportion. Mr. Watkins, however, showed that under many conditions of development the particles were not all acted upon simultaneously, but that there was a considerable amount of action in the high lights

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before there was any change in the shadows. diagrams tended to show what he thought Mr. Watkins would like to show rather than the fact which he demonstrated in the actual experiments. With regard to the control obtained by the use of bromide and by altering the concentration of the developer, he thought a good deal of control could be obtained; and, indeed, Mr. Watkins's experiments seemed to demonstrate this. The tendency of many people in the past appeared to have been to imagine that a good deal more control was obtained than was the case; but the tendency now he thought was in the opposite direction, people denying that one had control at all. The latter fact, however, was amply proved by Mr. Watkins, who had explained in a fair way that one could get over the difficulty of over-exposure, if one only knew the fact beforehand, by the introduction of bromide. But it was said that bromide was of little use unless put in at first. That seemed to him, (Mr. C. Jones) a statement which was very difficult to prove. If one started development and washed off the developer before it went too far, then it was possible to substitute a slow acting developer. At any rate, it was difficult to prove that it was not possible. With regard to developing a long series of negatives for the same time and getting useful results, that had been argued a good deal lately, and he thought the two extremists both wrong. Under certain circumstances, if one developed negatives having various exposures for the same time there would be obtained many spoilt negatives; but if negatives all tended to under-exposure, which was the usual case in kodaks and such like cameras, it was impossible in many cases to over-develop. There was no further change unless the film remained so long that there was fogging, and the fogging could be easily distinguished from the developing stage. He understood Mr. Watkins to say that one could deal with over. exposure but not with under-exposure. He thought that quite wrong, as Mr. Watkins himself appeared to have shown. Of course that which was not on a plate could not be developed from it, but in many plates there was a tendency to get a great density in the high lights before the detail and shadows had appeared, but by using a judicious developer, which brought out the details first, a harmonious range of gradations could be obtained, and the operator could stop at any stage he wished.

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Mr. J. H. GEAR said he did not hold with hard and fast time development, but whenever he had adopted time development he had always succeeded with his plates. A very considerable advantage in the timing of development was found when dealing with tricolour work. He did not know how it was possible to develop three negatives with equal opacity where there was a different range of gra dations, so to speak, caused by the various colours, and he felt that the timing method under such circum

stances was the only reliable system in order to get the three colours at their correct opacity. With regard to the alteration in the factorial time, he had found plates of the same manufacture vary somewhat, for instance, Lumiere's A. plates, and their B. plates, and the plate sensitive to red. Taking the factor of 4 for the A. plate and also for the red plate, that did not give the same opacity as the green plate; and in order to develop those plates with the factor, he had found it absolutely necessary to take 4 for the blue plate, 4 for the red plate, while 3 gave the same opacity for the green plate. He thought it must be admitted that there was not the control in development which had been previously imagined, if one adhered to the pyro and soda developer. He had no doubt that bromide had but little effect after once commencing development, and he would not expect to get the control in the development by the addition of bromide. but by the addition of sodium citrate. He felt the sodium citrate was practically the only control they possessed. When the plate was over-exposed, the results were as Mr. Watkins had shown.

Rev. F. C. LAMBERT said he felt the following difficulty. If he had a slow plate giving a considerable range of exposure, was he to understand that one had to take the time from the pouring on of the developer to its first appearance, and multiply that for a constant factor under all conditions? Suppose the image appeared in ten seconds, and the factor was six, he must develop for one minute; if with that plate he gave the shortest possible exposure, and gave the other half of the plate the longest possible exposure, he would expect under those conditions that the time of the appearance of the image would be different; the more brief the exposure the slower would be the picture in appearing; but if he used the same factor in both cases, would he get the same result? He anticipated an opposite result, because he imagined that for the same degree of contrast, the longer exposure, which came out first, should have the higher multiplying factor.

Mr. W. THOMAS, speaking as an ordinary practical photographer, said that what one wanted, as a rule, was the maximum result from light action in the shadows, and a very considerable stage of that maximum result of light action in higher stages. He thought highly of the work done by Mr. Watkins, and while agreeing with almost everything he had laid down, he could not bring himself to find that his own practice was in accordance with those doctrines. Taking a subject with white and as near dark as could be got, some parts lit with clear brilliant sunlight and the others in the shade, there was something to deal with beyond those; there was such a thing as light and shade, and such a thing as colour. Colour entered into such matters in a very important way, and he thought it was not taken sufficient note of in escriptions and lectures on the subject. It seemed

strange to say that the results produced could not be altered and varied, and he said so with the more confidence after what he had heard that evening. He thought if there was lacking proof that control was possible and existed, that proof had been furnished by Mr. Watkins himself. With regard to the addition of bromide after the development had commenced, he understood the reader of the paper to say the result of his work had been to convince him that no saving alteration could be brought about by the addition of bromide once development had commenced. Such an experience was opposed to his own.

Mr. FRIESE GREENE agreed that the bromide in the developer had only a kind of mechanical, and not a chemical action, but he wanted to bring before the meeting the fact that if the continuous electric current were introduced at the beginning of the development where bromide was used it seemed to enhance the retarding action of the bromide.

The CHAIRMAN said Mr. Chapman Jones had dealt with much that he had intended touching upon. Everyone must admire the great care with which Mr. Watkins had conducted and recorded his experiments on development, and that gentleman had cast a new light on many manipulations in that process. Mr. Watkins had shown that there was a factor, which, if used, would enable the photographer always to arrive at the same degree or intensity of gradation. Of course there was a certain difficulty in arriving at a factor. For instance, what was the first appearance? That was to a large extent a question of a personal equation, and with that he fully agreed. One person would see a black speck coming out on a negative before another person. He had often developed side by side with his assistants and friends, and it had often been difficult to decide at what exact time the image appeared. But that could be got over, and when once the personal equation had been arrived at, one could have a factor for different kinds of plates for development. He had made a great many experiments, and he had come to the conclusion that there was a great deal more control in developing a negative than Mr. Watkins liked to allow. He was not a professional photographer, and therefore he did not develop the plates because he was obliged to, but he looked upon the development of every plate as a kind of experiment; and if anything remarkable occurred during the process he repeated it to see what it meant. At the time of Hurter and Driffield's paper, there was a great controversy as to whether there could be an alteration brought about by variation of the developer. He had neither the time nor the inclination to enter into that controversy; he had a controversy on another point with those same gentlemen, but the experiments he had carried out left him no doubt, that there was a control in development by means of varying the developer. On the screen was represented development by means of metol, and one by ortol. If one exposed two strips, as he had himself

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