THE BRITISH JOURNAL OF PHOTOGRAPHY. Vol. XI, No. 238, November 25, 1864,
THE TOOVYTYPE, OR THE PROCESS OF PRINTING ON WHITE GLASS.
WE have lately been making some experiments in. Mr. Wenderoth's "Toovytype process," of which a. general sketch was given in our last number-[ante-page 458]. The first and (as it turned out) the only difficulty, we had to encounter in working out the details of this process was that of procuring the proper quality of glass. The opal glass generally sold in this country is, very irregular and lumpy on the surface, the effect of which is that the albumen cannot be distributed evenly over it; and for the same reason the plate itself cannot be pressed in close contact with the negative. This of course precludes the possibility of obtaining a regularly-printed and well. defined proof.
The only samples we could procure fit for the purpose, were at a photographic warehouse, from some very old stock which had never previously, been put to any practical use, and the only portion of these which could be of any service was that which had been, ground on the surface, and thus rendered quite flat and free from striae.
After selecting the glass, we found, after a few preliminary experiments, the following every; convenient mode of operating:--
To Prepare the Albumen:--Put the whites of three fresh eggs into a clean ten-ounce bottle; add thirty grains chloride of ammonium or sodium and three or four drops of strong ammonia. The latter is for the purpose of rendering the albumen more limpid and less stringy. Shake violently till; the whole has been beaten into, a froth. Allow to stand for twenty-four hours; then filter through three or four folds of muslin into a small stock-bottle. The albumen is now ready for use.
The ground surface of the opal glass may be prepared for receiving the albumen coating by brushing its surface, under a running tap, with an old tooth or nail-brush (which, however, must be free from soap, &c.), and then standing it up to dry. When dry, pour on the surface destined to receive the image a small pool of the prepared albumen and spread with a glass rod or camel's-hair brush, taking care to remove to the side of the plate all air-bubbles and particles of dust. Then tilt back into the stock-bottle all the superfluous albumen in the same way as when finishing the coating of a collodionised plate. When sufficiently drained, stand up the plate in a place free from dust on a piece of clean blotting paper and allow -it to dry spontaneously. The film is so excessively thin. that; if dried by artificial heat, iridescent .rings will appear all over the surface. These rings do not disappear after the subsequent operations are completed.
To Excite the Film.--After the plate has become quite dry plunge it into an ordinary seventy-grain -nitrate of silver bath used for exciting positive albumenised paper; but it must be carefully filtered before use, because any scum or dirt from it adhering to the ground surface cannot afterwards be removed without danger to the film of albumen. Allow it to remain in the bath for two minutes, and then stand up in the dark to dry spontaneously, as before, on .a piece of clean blotting-paper. In this case, also, artificial heat is injurious, from its tendency to cause crystals of nitrate of silver to form on the surface. These, if: present, will be plainly visible when the plate is thoroughly dry. In such a case, they must be removed by lightly brushing the surface with a brood, camel's-hairbrush before the plate is placed in contact with the negative.
The Exposure.--The printing is performed in the same way as with the ordinary albumenised, paper, by placing the sensitive side of the opal glass in close contact with. the negative in the printing frame, and exposing to daylight as usual. The only difficulty attending this operation is than we cannot lift up the glass as we can do with paper; to judge of the depth to which the printing has reached. According to our own experience, the time of exposure required when using the above solutions is about two-thirds longer than that necessary for paper prepared by the same solutions, or in the ratio of three to five in favour of the paper.
Toning the Picture.--When removed from the printing-frame the plate is well washed on both sides under a running tap, for the purpose of removing all the free nitrate of silver previous to toning. The toning is quickly effected by immersing the glass in an alkaline gold toning bath prepared by any of the well-known methods. A simple bath of weak gold, rendered slightly alkaline with bicarbonate of soda, answers all requirements, for there is no chance whatever of mealiness or red spots in the process.
Fix, in strong hyposulphite of soda--say eight ounces to the pint of water. A strong fixing bath we consider important, because the energetic solvent action of a concentrated solution on the albuminate and chloride of silver--which are the only silver salts present, except, perhaps, the oxide--prevents tine possibility of hyposulphite of silver being formed in the film; and thus laying the, foundation of future decay. Five minutes in this bath is sufficient.
Finally wash freely in plenty, of water, and set aside to dry,
The, picture is now finished, and, if all the operations have been carefully performed, it will be found far superior to any print from the same negative on albumenised paper--not only in delicacy and harmony of outline and half-tone; but, in possessing an ivory sort of softness in the whites: and a transparency in the shadows which no other printing process known to us will render nearly so well.
The class, of negative we have; found best suited for the Toovytype process is that which contains good detail and half-tone, without much density in the high lights. From the slowness of the printing compared with that of .paper, negatives of too great intensity are somewhat apt to give chalky whites, the half-tone terminating too abruptly. This we find hardly remedied by continuing the exposure for a longer period; but, no matter how long; it be protracted, there is always a transparency in the shadows which with similar depth of printing on very sensitive paper would be entirely obliterated in one black mass.
The ground white glass is eminently suited for coloured portraits. We are assured by an artist who has made some experiments with these pictures that they take the colour admirably, and; when finished, they possess all the transparency and brilliancy of ivory miniatures.
We have not been able to experiment on polished white glass plates, from being unable to obtain any specimens free from the irregularities of surface already referred to, which render them unfit for being placed in contact with a negative. But `no doubt if there arise a demand for this style of portraiture there will soon be a plentiful supply.
The process on ground opal glass is not altogether new in this country. On December 3rd, 1863, Mr. Forrest, of Liverpool, read a paper on the subject at a meeting of the Historic. Society of Lancashire and Cheshire, and also showed some specimens by Mr. Helsby. In this paper no details whatever were given, nor information on other points connected with these pictures which might have been serviceable; to other photographers. From what we can gather from Mr. Forrest's remarks they were intended to be viewed as transparencies.
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