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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1277, February 23, 1883
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The photographic news
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Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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118 THE PHOTOGRAPHIC NEWS. LFEBRTARY 23, 1883. ducing action of hmatoxylin under proper control, there is certainly little to be desired as regards the physical con stitution of the image. Whether the fine grained character of the deposit will lead to want of density has yet to be determined. Chemical Nature of Hamatoxylin —Some may feel inclined to institute some investigations concerning alkaline hoematoxylin. I will therefore briefly describe its leading chemical features. Hcematoxylin may be regarded as a natural phenol colour, having the composition C,H1O, It exists in logwood, and may be obtained by the following process recommended by Erdmann:—The commercial extract of logwood is mixed with quartz-sand to prevent agglomera tion. Five or six times its volume of ether is added, and the mixture agitated from time to time. After a few days a brownish-yellow solution is decanted off, and evaporated to a syrup, which, when mixed with water, deposits straw- coloured needles of hoematoxylin in a few days. Extract of logwood thus treated yields from one-eighth to one tenth of its weight of this substance. It dissolves sparingly in cold water, readily in boiling water, and in alcohol or ether. The solution speedily turns red, especially in day-light, and is rapidly converted by oxidising agents into hoematein C1H,20, A similar reaction goes on during development with hoematoxylin in presence of ammonia. The change may be represented by the following equation :— Hmatoxylin. Ammonia Hmateate, 2CiH10++4NH3+0,=2H,0+2(NHa,C16,H,206) A solution of hcematoxylin in ordinary water appears to lose its energy as a developer after a time, its red colour changing to purple, owing to oxidation. Probably, how ever, the alcoholic solution would keep longer. By fusing hcematoxylin with caustic potash it yields pyrogallol; and colouring matters analogous to hoema toxylin, called the phenol-colours, are procured by heating carbolic acid with polybasic organic acids. In conclusion, it would be well to mention that the expense of hcematoxylin, as prepared commercially, is far too great to permit of its extensive use by photographers : it is even more expensive than hydro-quinone, costing more per dram than the latter does per ounce. Another objection to its employment is the trouble which it gives in dyeing and staining everything with which it comes into contact. FRENCH CORRESPONDENCE. MM. Ch. CRos and VERGERAUD’s Positive Paper—M. Lamy’s Gelatino-Bromide Paper—Thiebaut’s Pelli cle Paper—The Pellicle Competition. MM. Cros and Vergeraud's Positive Paper.—MM. Cros and Vergeraud have worked out a process for obtaining images so as to have a positive impression from a positive plate, and a negative print from a negative original. The process is based on the following circumstances : the easy reduction of soluble bichromates mixed with certain organic substances, and the relative insolubility of bichromate of silver. Suitable paper is covered with a solution of two grammes of bichromate of ammonia, and fifteen grammes grape-sugar, dissolved in 100 of water ; when dry, it is ex posed to light under a positive. As soon as the yellow paper becomes grey, it is removed, and immersed in a one per cent, silver bath, to which ten per cent, of acetic acid has been added. The image will immediately appear of a ruddy hue, due to the bichromate of silver. The print, on being washed, retains the red impression of the insoluble bichromate, which becomes dark brown on exposure to sun light. On submitting the print when dry to the fumes of sulphuretted hydrogen, or dipping in a solution of sulphite of copper and potash, it becomes black. The latter process is preferable. M. Lamy's Gelatino-Bromide Paper.—While on this sub ject, a few words must be said on M. Lamy’s brilliant paper for positive printing. This paper receives mechanically a film of gelatin o-bromide of silver, and, contrary to Morgan’s for negative printing, gives excellent positive images, and suitable for gold toning. A certain number of well-known photographers have employed it with great success. On the other hand, Morgan’s paper is becoming more and more highly appreciated. In certain parts of the country, amateurs use nothing else for their negatives. It offers the advantage of replacing heavy plates, and the negatives obtained are equal to glass in delicacy, because the film is of a fine regular texture. As soon as Mr. Morgan shall have perfected it, so that the film may be stripped off and transferred to glass, gelatine, celludoid, or some other trans parent vehicle, its use will be much more general for indus trial purposes. M. Thiebaut's Pellicle Paper.—M. Thiebaut manufactures pellicle paper of this kind, and is successful; he would not compete for the thousand franc prize because he wished to reserve his process. The Pellicle Competition.—This competition closed on December 10th last, and was not large, only three or four hav ing entered for it. The commission appointed to judge the results are at work upon the subject now. It is much to be desired that paper pellicles should be produced of uniform good quality, and that frames and portfolios for enclosing them be improved in make. It would be an excellent plan if the pellicle could be placed in direct contact with the ground glass, thereby simplifying luggage and reducing weight, besides affording an exact method of focussing accurately. It is indispensable that the sensitized pellicle should adhere closely to the glass, otherwise the reflected image diffused over the ground glass surface will not be reproduced sharply. MARION’S FERRO-PRUSSIATE PROCESS. BY EDGAR GOOLD.* This process, which I have been invited by your secretary to illustrate, offers great advantages to engineers, architects, and others, for the reproducing of drawings, patterns, plans, &c. No complicated apparatus is necessary to work it, no poisonous substances or dangerous acids are used, it does not need very great care, nor does it require the use of a photometer in the printing ; and last, but not least, as far as time and labour go, it requires neither toning nor fixing, but, after being exposed to actinic light in the printing frame, it is only necessary to wash with water, which speedily gives a white line on a blue ground, the transparent parts of the drawing to be reproduced giving a blue ground, while the opaque parts give the white lines; the greater the amount of actinic light to which the print has been subjected, the deeper the blue. There is another way of working the process so as to obtain a blue line on a white ground ; but to do this, a negative must be made on a special paper, supplied for that purpose, and is known by the name of Mince. In very bright sunshine the exposure required varies from five to ten minutes, while in the very dull days of winter it may need two or three hours, or even a whole day. The exposure required to make negatives is at least three or four times the length of time necessary to make positives. While printing, the “ ferro paper ’ ’ assumes various tints, changing from yellow to greenish blue, then to bluish grey, and last to an olive colour. When it arrives at this stage the exposure must be stopped. The printing frame need not be opened to ascertain the progress of printing, but can be judged by the margin of the paper, which, of course, must be little larger than the tracing under which it has been placed. The washing can be effected in any room. The print is taken from the frame and immersed in clean water until the lines become purely white, the time for washing occupying from five to ten minutes. Over-washing reduces the intensity of the blue ground. The prints are afterwards suspended over a wooden bar to dry, and if the prints aie very large in size, some difficulty will be found in lifting them from the washing trough without tearing them. Frequently I have prints from five to six feet long • Read before the Newcastle-on-Tyne and Northern Counties Photo- graphic Association.
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