  NEGATIVE PROCESS—SOLUBLE COTTON—PLAIN COLLODION—DEVELOPING SOLUTION—RE-DEVELOPING SOLUTION—FIXING THE IMAGE—FINISHING THE IMAGE—NITRATE OF SILVER BATH. Negative Process. The manipulations and chemicals employed in the production of the negative collodion pictures are very similar to those already given for operating by the positive process; frequent reference will therefore necessarily be made to portions of that process, as described in the preceding pages, and only such parts will be given here, as do not correspond with the foregoing. It is thought advisable to omit in this chapter every reference that does not have a desired tendency to aid the operator in the plain straightforward order of manipulation. The negative process is fast becoming popular and needs the attention of all who desire to keep pace with the experiments in the art. Since the first edition of this work it has been my pleasure to see many fine photographic specimens produced by the following process, and no There perhaps may be circumstances making it advisable for some to have but one nitrate of silver solution for both positive and negative collodion pictures: for such, a process will be given in the following pages, which has recently appeared in Humphrey's Journal, and is called, after its author, the "Helio Process," this is well adapted for most purposes. Soluble Cotton. The method for preparing this has been given in page 41. It is prepared in the same manner for both positives and negatives. Plain Collodion. The preparation of plain collodion employed is the same as that described at page 53. Developing Solution for Negatives.
A little alcohol may be added to make it flow more evenly over the plate—say 1 oz. This solution can be kept in a pint bottle, and should have a funnel devoted solely to the purpose of filtering it. One of the most convenient dishes for receiving this solution, when poured over the plate, is a bowl with a lip to it, as it can be readily poured back into the funnel. The mode of employing this developer is the same as that for positives, described at page 133. It may be used an indefinite number of times, but should be kept clean; it soon assumes a red color. Re-developing Solution. This solution is for the purpose of giving increased intensity to the negative, but as its use in the hands of beginners is attended with some difficulty, I would not recommend the operator to try it until he has had considerable experience in the developing process, or he will undoubtedly spoil his proofs. Its use requires promptness of action and quick observation. The following is the formula for its preparation:
Put this into a bottle, and when the crystals are dissolved, it is ready for use. It should be kept filtered, and can be used only once. Now in another bottle put
Remarks.—The impression is to be well washed after the developing solution has been poured off, and then the re-developing solution (that portion containing the protosulphate of iron) can be poured on—the plate being held perfectly level: the surface is completely covered; the water containing the nitrate of silver should then be poured rapidly on, to mix with the iron, when the surface of the impression will instantly commence to blacken; and if the It is a matter worthy of notice, that there is no perceptible action when the iron solution is poured over the glass; but the action is very energetic the instant the nitrate of silver solution comes in contact with the iron salt and the silver. As soon as any change can be observed, after the re-developer has been poured over the plate, it should be quickly and copiously washed off with clean water, and then it is ready for the fixing process. I would dissuade novices in the art from practising with the re-developing solution, until they have first thoroughly mastered the entire process of taking negatives. The developing solution is the only one used by operators generally, and will, with proper care, produce satisfactory results. Fixing the Image.
Remarks.—This is nearly a saturated solution. The glass can be put in a dish and the solution poured over, or held in the hand, in the same way as the plate in the daguerreotype process. It can readily be seen when a sufficient action has been attained, as the unaltered bromo-iodide of silver will be dissolved, leaving only the reduced surface holding the image. This action should not be continued too long, as it affects the intensity of the picture, injuring it for printing. The glass should be well washed by pouring over it clean water, and then it can be stood away to dry, in a Finishing the Image. This is done with the same material, and in the same manner, as that given for positives—page 134. Remarks.—The glass negatives, when not wanted for use, should be carefully put aside in a box, and kept free from dust and dampness: by so doing, it is believed that they will remain good for any length of time. Nitrate of Silver Bath. This solution differs only from the positive bath, by omitting the nitric acid: in all other respects it is precisely the same, and is prepared by the same formula, as given at page 64. This is called the neutral bath, and is best adapted to the negative process. The nitrate of silver employed in its preparation should be perfectly free from excess of nitric acid, otherwise the whole solution will be slightly acid. If it should not be convenient to obtain nitrate of silver without this objection, the acid may be neutralized by putting into the solution a small quantity of common washing soda— say 1 grain to each 100 grains of nitrate of silver—previously dissolved in about half an ounce of water. This may be put in at the same time that the iodide of potassium is, and it would save one filtration. In twenty samples of nitrate of silver that I have tried This bath will improve by age, and be less liable to fog after having been in constant use for one or two weeks. Operators who have the means, and design following the art professionally, will find it to their advantage to make from two to three times the quantity of solution they require for immediate use: by this means they will be enabled to replenish their stock, which may be used up or otherwise lost. OF THE PRINTING PROCESS.
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