The Optical Magic Lantern Journal (August 1890)

18 The Optical Magio Lantern Journal and Photographic Enlarger. page, states that he has an improved oxy-calcium jet of 300 c.p., which dispenses with coal gas, is simple to use, and can be employed for dissolving lanterns. 2 * 2 Ir appears that stereoscopic photography is reviving in Sheffield, as the Photographic Society of that town have purchased several stereoscopes for use at their meetings. Stereoscopic negatives are well adapted for contact printing for lantern transparencies. ? ba * It is with regret that we have to announce the death of the Rev. T. F. Hardwich, which took place on June 24 at Shotton Vicarage, co. Durham. Mr. Hardwich, who was an authority on optical lantern matters, was a contributor to our columns. 105 Toning Transparencies. ALTHOUGH in many cases a wet collodion transparency is of a tone sufficiently good to need no toning, yet is the lightness of the colour of the deposited silver of which the image is composed not pleasant to the eye, a dark if not black deposit being invariably preferred. The blackest colour is obtained by immersing the transparency in a weak solution of chloride of platinum, in connection with which two things must be observed—first, that it is rendered acid by nitric acid; and secondly, that the toning bath be exceedingly weak. Having dissolved the contents of a 15-grain tube of chloride in 20z. of water, add thereto drop by drop a solution of bicarbonate of soda of which the strength is not material, until after stirring well with a glass rod the solution of platina no longer reddens litmus paper, which it will certainly do previous to the addition of the bicarbonate of soda. The hydrochloric acid being thus neutralised, one or more drops of nitric acid must be added, until the blue litmus paper turns red, and shows that the solution is once more acid. Bearing in mind how many grains of platinum the solution contains, viz., fifteen (or more or less), add one-fifteenth of the solution to 15o0zs. of water, which will give a toning bath containing one grain of platinum chloride in 1Sozs. of water. The transparency is immersed in this, and allowed to remain until the yellowish colour of the silver image is changed to a black tone. When looked through, the tone will be found to have become a neutral black. The transparency is then rinsed in water and allowed to dry. A black tone of a rather cold nature, although it answers well for portraits, may also be given by immersing the slide in a very weak solution of bichloride of mercury. The first action of this toning solution is to blacken the picture, which after arriving at this stage begins gradually to bleach. But the mercury solution, like that of the platina just described, must be so weak as to enable the operator to leisurely remove it from the toning bath when once it is seen to have become blackened through and through, and place it in water so as to entirely wash out every trace of mercury. If this is done all further action is arrested, and the transparency when dried may be looked upon as permanent. Some prefer to keep the plate in the toning bath until the bleaching action has set in, when it is removed, washed very thoroughly, and placed in water containing two or three drops of sulphide of ammonium, by which a rich brown colour is produced. It is unnecessary to say that washing must follow this treatment. A plain solution of chloride of gold also acts as a good toning agent. While some use this by itself, others prefer to mix it with a solution of bichloride of mercury, in the belief that it may conduce to greater permanency. Sulphide of potassium or liver of sulphur is much employed in the toning of transparencies on account of the fine purple-brown colour it gives. Its offensive smell is its most objectionable feature; but as the solution ought to be very weak, and the toning process can be conducted near to achimney, or even out of doors, no inconvenience need really be experienced from this cause. The toning action commences as soon as the plate is placed in the solution, and proceeds with a degree of rapidity in proportion to the strength of the bath. It should be borne in mind that this solution not only tones, but also intensifies the image, and hence it is necessary that the transparencies that are thus toned should be rather thin. Some, as in cases previously cited, add chloride of gold solution to the sulphide toning bath; others recommend in addition: albumen that has been liquefied by being shaken up to a froth, with a few drops of ammonia, and then allowed to stand until liquefaction takes place; gelatine, gum, and substances of like nature. It is the potassium sulphide, however, that is the active toning agent. Singular though it may seem, collodion transparencies toned by this agent not only possess a high degree of beauty, but also a greater degree of permanence than those by many other systems, for it is generally known that silver sulphide is one of the most stable silver compounds. It may sometimes happen that a transparency of a pronounced reddish brown colour is wanted, as when one has got some enlarged or micro