334. If the exposure has been too short, that is to say, if in thirty seconds the high - lights do not yet appear, add drop by drop, and with the greatest precaution a little of the solution A. If the exposure has been too long, that is to say, if the high-lights appear suddenly and before the thirty seconds, add without delay a few drops of the solution B. In order that the addition of this solution B should produce the desired effect, it is necessary that it should be done as soon as the excess of exposure is discovered. In this case the development taking place with the greatest rapidity, it is necessary, in order to save the print, to retard the development from the start. If you wish to give more intensity to the negative, add a few cubic centimeters (one cubic centimeter is equal to sixteen minims) of the solution of pyrogallic acid No. 1. Now finish as just explained after the iron development. Thus with pyrogallic acid it is possible, and this is of very great importance, to correct the excess or the insufficiency of exposure. To reach the same result with iron, it is necessary to operate in the following manner: If the exposure has lasted any too long, as soon as you perceive it, add at once a few drops of bromide may be remedied by increasing the quantity of potassium bromide in the same ratio as that of ammonia, thus ultimately correcting defects due to errors of exposure or faults in the emulsion. A milky veil is sometimes seen when the ferrous - oxalate developer is employed. It is due to a precipitate of oxalate of lime formed by the oxalic acid of the developer coming into contact with the lime of the hard spring water in which the plates have been washed. "With the pyrogallic developer this chalky precipitate does not occur, even when spring water is used, for caustic ammonia only precipitates lime after a lapse of some time. It is, however, always preferable to use distilled water for the purpose of washing - or, at least, rain water. As a remedy against solarization, avoid as much as possible too great'contrasts in the image to be produced; place the camera so that no reflection of light can penetrate the objective; do not prolong the exposure more than necessary; stop the development as soon as possible, and blacken the interior of the dark slide and the back of the plate. - W. P. Bolton. 334. I name the ingredients of an intensifying solution which I have found exceedingly useful in my hands. There is nothing new about it, save in the combination of the chemicals, so far as I am aware; but there is great latitude in their use, and by varying the proportions wide diversity of effects may be produced. It is needless to give proportions. I therefore leave the reader to experiment, and find them to suit himself - now more of this and less of that - as circumstances may demand. Take bichloride of mercury, iodide of potassium, and cyanide of potassium, and mix with intelligence. With these three old - fashioned agents capital results may be got, and the solution may be used again and again till exhausted. I reduce over-intensity with chloride of copper, cautiously followed by ammonia; but the less there is to reduce the better. It will be found that a surface deposit takes place upon most negatives when intensified, but this is easily removed by a gentle rubbing with the finger or a soft brush. This may be done also with advantage after all washings. - G. G. Mitchell.
Since the adoption of the gelatin process in lieu of collodion, one of the troubles which, when it occurred, has been the most difficult to cure, has been the occasional production of too intense a negative. I have now to offer a remedy which I have found thoroughly effective, reducing in an even manner, and without destroying the half - tones, a negative which had resisted even strong cyanide. The agent I employ is "Holmes' Ozone Bleach" - an article sold for laundry and disinfectant purposes at eightpence per quart bottle. I use this diluted with about four times its bulk of water in a dish; greater or less strength may, of course, be used as desired. If to bring down locally any particular part of the negative, a little of the undiluted liquid may be poured on the plate already swilled with the weaker solution; but in this case the tap must be handy to stop the action quickly when wanted. The same solution (perhaps more diluted) may be used to discharge the last trace of hypo from the plate for those who prefer to intensify with silver and pyro. - W. E. Debenham.
The thorough elimination of hyposulphite of soda from gelatin negatives ought to be done with a great deal more care than is generally the case, and many good negatives are lost through inattention to this important point. The negatives, after having been thoroughly rinsed under the tap, ought to be laid, face down, in a dish, or, what is better, a zinc trough made with sloping sides, the bottom being narrower than the top. A small bole near the bottom of one side will let out the water, which should be run in from a tap in a constant stream for an hour or two upon the negatives. The outlet should, of course, be leas than the inflow in order to keep the trough full and covering the negatives. Having been annoyed by the long time my gelatin negatives took to dry, I hit upon the following plan by which they may he thoroughly dried in a few hours. It is simply to set the negatives in sunshine, and with a good breeze it will be found that they dry thus both quickly and well. Care must, however, be taken to guard against rain falling on the half - dried plates, which, if it occur, would completely spoil them. - John Jackson.
The beginner will doubtless find this developer very convenient, as it dispenses with the use of ammonia, which is rather difficult to use; but when he shall have acquired more experience, he will not hesitate, in order to increase the intensity and correct the exposure, to have recourse to the two drop-bottles of ammonia and bromide already recommended for the alkaline development. Beer, used in the proportions of one - fourth or one-half, in the developer produces results rather remarkable and analogous to those of the bromide; it gives brilliancy and intensity to the negative, but retards slightly the development. The sucrate of lime, recommended by Mr. Davanne, added in small quantity either to the iron or to the pyrogallic acid, gives nearly the same results as the bromide and the beer, but appears to have over these two substances the advantage of not retarding the development. When used, it is necessary to filter the developer after it has been added to it.