This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Sulphite of Soda (Anhydrous). . .
Carbonate of Soda (Anhydrous)
.......... 5 drams
Ascertaining Factor. The factor of this formula is ten. In this formula we have two developing agents - metol and hydroquinone; and we have sixty grains of hydro-quinone, or four times as many grains of hydroquinone as we have metol, the latter of which we have fifteen grains. These developing agents, as formerly stated, having different factors, we must ascertain the proportions used of each agent to the developer, and our factor is regulated accordingly. The factor of hydroquinone we know from the table of factors is "five," and for metol is "thirty."
472. Where we desire to take two different developing agents and combine them into one developing solution, the factor is approximately the average of the two constituents if in equal parts. Thus, with hydroquinone " five" and metol " thirty," if used in equal parts, the average will be " seventeen and one-half," but if the combined developer, as in this formula, contains four parts hydroquinone to one part metol (five parts in all), we must add the factors for all five parts (the factor for each part being the original factor for that particular developing agent), and divide by the total number of parts; thus 5+5+5+5+30/5 =10 Any combination of long factor developers can be obtained in this way, but a combination developer containing pyro does not conform to this rule, and its factor must be ascertained by actual trial.
473. A few facts should be remembered: The factor of all developers, except pyro and amidol, depends upon the developing agent, and not upon the formula. The varying of the quantity of water, or increase in alkali, or even the use of bromide, may alter the time of the appearance of the image, but does not alter the effect of the long factor developing agents, such as metol, etc. Temperature effects the time of appearance, but does not modify the factor; however, with pyro and amidol for short factor developers the factor varies with the strength in grains to the ounce solution, but in all other developers the factor does not alter with strength or dilution.
Retaining Normal Temperature. While under ordinary conditions one can work with an average temperature of from sixty to seventy degrees Fahr., yet there are times in very hot climates that the temperature is very high. In such cases a quick developer is preferable, for the quicker you can completely develop plates, fix and wash them, the better it will be for the resulting negative. However, where slow development is preferred one can, if they wish to go to the little extra trouble, arrange their baths so as to hold them at a certain temperature throughout the entire time of developing. First of all, the developing room should be kept cool, and by providing a "water bath" into which you place your developing tray, you can hold the developer to the temperature of the water.
475. If the temperature of the water is high, then the addition of a little ice in the "water bath" will reduce it to the proper state. For example, take a tray or dish larger than your developing tray and place water in this large tray, having the temperature of the "water bath" lower than normal, say 60 degrees Fahr., and if the temperature of the room is 68 or 70 degrees Fahr., place your tray containing the developer in this ' water bath," and after a few minutes you will find the developing bath will become about normal, or 65 degrees. In cold weather the same method may be employed. Instead of using cold water, however, in the "water bath," sufficient warm water can be used to raise the temperature as much above that of your developer, or developing bath, as the temperature of the room is below normal, thus equalizing the temperature.
MARINE Study No. 10 S. I. Carpenter.
The above suggestions are intended for extreme cases only. Under ordinary conditions the extra "water bath" will be unnecessary.
476. In making your experiments with factorial development, after carefully reading the instruction for obtaining factors, etc., it is advisable for you to try out the formula given. First try the pyro formula, and after providing yourself with a few normally exposed plates, then proceed to prepare your pyro developer exactly according to the formula given. When you are ready to develop note the time by your watch, and at once place the plate in the developer, and observe the image as it appears. When the strongest highlights are clear, and the general outline slightly visible at this stage, take the time again and note the number of seconds it has required for the time of appearance, for this is the key to the proper results. Multiply this time by your factor, which will indicate the total time required for complete development. By applying the factor given in this instruction, the only mistake you are likely to make is in judging the time of appearance; and this you can become accurate in by experience and intelligent experimenting only.
477. After your first experiment, dry the negatives, and make proof prints from them, and note the results. Note on the back of the proofs the date, first or second trial, as the case may be. Note the time of appearance, the developer used, the factor employed, total time of development, and any other data that can be used for future reference. File these proofs in your letter file, under the title "factorial development." After a few experiments with our regular formula, change the formula and obtain a new factor, keeping a record of the change. Make proofs from each resulting negative, note formula on back of proofs, and the necessary data, and file as usual. In this way you will have a practical record of all your experiments.
478. After experimenting with the pyro formula, next.
take up the metol - hydroquinone developer, and make your experiments, and prove all your results in like manner, making careful note of each experiment, and number each proof so that you can note your improvements from the first to the last.