Positives. Photographic positives, such as transparencies for windows and for the magic lantern, are very popular, and continue to be made by methods given in Lesson W. A few more hints are given here.
And the almost universal use of the bromo-gelatine-emulsion plate for negative making, causing all who could to discard the nitrate of silver bath or " wet" method, has encouraged the introduction of another process for the production of positives in a quick way, and by the use of may not be in actual contact over three-fourths of their surface, there will be no loss of sharpness; to try this, I have separated the two plates with pieces of thick card, and still no loss of sharpness; in fact, before dry plates were used, I had made hundreds of wet-plate negatives in this way from transparencies where the two plates were separated by corner pieces of stout silver wire.
The directions given for developing the transparency must be followed in developing the negative from it, being always careful to avoid underexposing. - Geo Hanmer Crouqhton, in the Philadelphia Photographer.
374. All must admit that in point of delicacy of gradation and minuteness of detail, a collodion positive on glass is as far superior to a paper print as a copper - plate engraving is to a wood - cut. Were it not for the facility of reproduction, paper prints would probably never have ousted the collodion positive from public favor.
It may interest many to know that pictures of almost precisely similar character may be obtained from ordinary bromo-iodized gelatine plates by the adoption of the foil wing treatment: Any ordinary dry plate is exposed in the usual manner, but for about half the time required for a negative. It is then developed with a ferrous-oxalate developer, made up as follows;
Ferrous Sulphate (saturated solution) .
Potassic Oxalate " "
Pour the oxalate solution into a measure glass, then the ferrous - sulphate, alter which add one or two drops of saturated solution of potassium bromide to each ounce of the mixture - not more. Develop carefully until the picture is all visible on the upper surface, then stop the development by washing in water. Fix. After fixing, alum the plate, if necessary; then rinse once with a very weak solution of chloride of lime to remove any hypo. After this the plate may be brought to the light, and immersed in a solution of bichloride of mercury, twenty which those who are asked for a single picture may produce it independent of the bath. I allude to the new Argentic positive process, by the use of which pictures obtained on an emulsion coating upon japanned iron plate. The manipulations are easy, the results are soft, and they will become more and more popular as their manipulation and manufacture is improved.
Of the many new and beautiful methods of photo - mechanical printing, only mere mention need be made here, as they are not available for the general reader of Photographics. Proofs of their excellence may be found in the current photographic magazines. Our appendix already contains enough to enable the reader to produce "all the new things in photography" worth his attention.
375. In apparatus, instruments, and appliances the changes have been infinite, so to speak. You must consult your dealer, whoever he may be, always remembering, that if you are in earnest with photography, "the best is the cheapest." grains to the ounce of water, until the picture has become quite white. Again the picture must be washed to remove excess of bichloride, and when dry may be varnished and backed up with Brunswick black, as is usual with collodion positives.
This process is invaluable for securing rapid pictures, and may often be used where too short an exposure has been given to insure a good printing negative, since from the positive a splendid camera copy ran be obtained, and intensified as a negative. This process may also be of service to our peripatetic brethren, who are industriously trying to get a living by taking rapid and cheap positives of "Arry" at the sea-side. - S. Bottone.
Almost any ammonia developer may be used successfully with the Argentic plates, but it is claimed that greater rapidity and more uniform results are obtained by using the Phoenix stock solution.
No. 1. Pyrogallic Acid ....
No. 2 Phoenix stock solution. (It is important that No. 2 be kept well corked.) Developer. -
This mixture may be used over and over, but each time will work slower.
An important thing in this new picture is to secure soft and pure whites. To do so, the development advised must be followed carefully.
The developing should be discontinued as soon as the outlines of the picture are fairly observable.
They should be permitted to remain in the fixing - bath until every trace of the bromide solution is eliminated.