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The photographic news
- Bandzählung
- 24.1880
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- 1880
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1146, August 20, 1880
- Digitalisat
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Zeitschrift
The photographic news
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Band 24.1880
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- Register Index 631
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Band 24.1880
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402 THE PHOTOGRAPHIC NEWS. [August 20, 1880. be 9yotograpgir Sehs. Vol. XXIV. No. 1146.-AUGUST 20, 1880. CONTENTS. page Photography In and Out of the Studio 397 At Home 398 The Preparation of Encaustic Photographs 399 Photography in America. By F. 400 What Can and Cannot be Patented 401 Mungo Ponton 402 New Iron Developers for Emulsions 402 Notes 403 Topics of the Day 405 The Preparation of Gelatine-Bromidc. By M. Bascher 405 Prints from Old Negatives 406 Photography by Gaslight. By P. Maitland Laws 406 Correspondence 407 Proceedings of Societies 407 Talk in the Studio 408 To Correspondents 408 MUNGO PONTON. On the 3rd inst. there died at Clifton a man whose name is as intimately connected with the history of photography as are those of Niepce, Daguerre, and Talbot. However much we may argue and dispute over the claims of this man, and that, to have discovered or modified important operations in the practice of photography, to the British chemist, Mungo Ponton, belongs undoubtedly the honour of having unearthed that key-stone upon which the perma nent printing processes of the present day are almost ex clusively based. In 1839—the very same year that the wonderful process of Daguerre was announced to the world — Mungo Ponton called attention to bichromate of potash as a photographic agent. Nay, more ; he described in the Edinburgh New Philosophical Journal a photographic process whereby permanent impressions upon paper might be produced ; and although these, viewed by the light of to-day, appear crude and primitive enough, they mark the commencement of an era in photographic science. Carbon printing—or, to speak more correctly, printing in pigments—collotype printing, and Woodburytype, all owe their origin to the discovery of Mungo Ponton, as do also, for the most part, the methods employed now-a-days for the production of ceramic photographs. We find the im pregnation of colloid substances with the bichromates of potassium or ammonium resorted to in every printing process we turn to, with the exception, of course, of the chloride of silver method, the platinotype, and one or two insignificant exceptions. The Mungo Ponton dis covery, we repeat, has had more to do with the produc tion of permanent photographs than any other, while it may safely be said that there is not at the present moment any satisfactory mechanical process in which the reaction he made public does not constitute the most important feature. It is interesting at this period of time to turn to the original memoir contributed by Mungo Ponton on the subject of securing photographs by the aid of bichromate of potash, which, as we have said, was first published in an Edinburgh journal. In reading it, many of our readers will be reminded of their school-days, when a sheet of paper was furtively washed over with the yellow liquid under shadow of the school desk, and exposed to light in the sunny playground. Fern leaves, lace, copy-book covers, nay, even the human hand, were employed in those days as negatives, the washed and dried prints being duly put away among other boyish treasures. Certainly Mungo Ponton’s was the first photographic process to become thoroughly popular. Here is Mungo Ponton’s original description of his method. “ When paper is immersed in the bichromate of potash, it is powerfully and rapidly acted on by the sun’s rays. When an object is laid in the usual way on this paper, the portion exposed to the light becomes tawny, passing more or less into a deep orange, according to the strength of the light. The portion covered by the object retains the ori ginal bright yellow tint which it had before exposure, and the object is thus represented yellow upon an orange ground, there being several gradations of shade, or tint, according to the greater or less degree of transparency in the different parts of the object. “ In this state, of course, the drawing, though very beautiful, is evanescent. To fix it, all that is required is careful immersion in water, when it will be found that those portions of the salt which have not been acted on by the light are readily dissolved out; while those which have been exposed to the light are completely fixed on the paper. By the second process the object is obtained white upon an orange ground and quite permanent. If exposed for many hours together in too strong sunshine, the colour of the ground is apt to lose in depth, but not more so than most other colouring matters. This action of light on the bichromate of potash differs from that upon the salts of silver. Those of the latter which are blackened by light are of themselves insoluble in water, and it is difficult to impregnate paper with them in a uniform manner. The blackening seems to be caused by the formation of oxide of silver. “ In the case of the bichromate of potash, again, that salt is exceedingly soluble, and paper can be easily saturated with it. The agency of light not only changes its colour, but deprives it of solubility, thus rendering it fixed in the paper. This action appears to consist in the disengagement of free chromic acid, which is of a deep red colour, and which seems to combine with the paper. This is rendered more probable from the circumstance that the neutral chromate exhibits no similar change. The best mode of preparing paper with bichromate of potash is to use a satu rated solution of that salt; soak the paper well in it, and then dry it rapidly at a brisk fire, excluding it from daylight. Paper thus prepared acquires a deep orange tint on expo sure to the sun. If the solution be less strong, or the drying less rapid, the colour will not be so deep. A pleasing variety may be made by using sulphate of indigo along with the bichromate of potash, the colour of the object and of the paper being then different shades of green. In this way, also, the object may be represented of a darker shade than the ground.” NEW IRON DEVELOPERS FOR EMULSIONS. Pursuing his recent investigations on developers, Mr. Carey Lea has discovered that there is a large number of salts of iron which possess developing power. He has tried ferro- phosphate, sulphite, and borate in solutions of potassium or ammonium oxalate, and expresses a highly favourable opinion on the developing action of all these salts on silver bromide. For dissolving the insoluble salts of iron the alkaline tartrates may also be used with advantage, the neutral tartrates of ammonium or sodium being more especially adapted for this purpose. Mr. Carey Lea’s researches have very great interest for the theory of photography, for they show thatferro-hyposulphite, metaphosphate, metapectate, antimono-tartrate, and other similar compounds, form more or less powerful developers; but when he goes on to attribute a value to these salts lor practical purposes, we find ourselves unable to agree with him. We tried in the first place the borate developer which he so strongly recommends:— Neutral potassium oxalato ... 400 grains Borax ... ... ... ... 100 „ Dissolve in hot water ... ... 4 ounces “ When completely dissolved, add ferrous sulphate, 120 graine. Add more water until the entire solution makes six ounces, and shake until the ferrous salt dissolves. Hetstand for six or eight hours, and filter. For use, dilute with three or four times its bulk of water,"
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