van Monckhoven, Désiré van. A Popular Treatise on Photography. Translated By W.H. Thornthwaite. London, 1863.
|Pure Nitrate of Silver||2 ounces.|
|Distilled or Rain Water||24 ounces.|
This liquid is filtered and poured into a gutta-percha tray. The collodion, spread upon the glass, is plunged into the nitrate of silver bath; the film whitens by the transformation of the iodide of cadmium into iodide of silver, which is sensitive to light, and it is in this state that it: should be exposed in the camera.
Such is a general statement of the process to be now described somewhat in detail.
Fig. 30. Coating the Plate.
The box containing the cleaned glasses being placed in the dark chamber, a plate is withdrawn , and the dust removed from the polished side by means of a large badger-hair brush, then holding the plate by one corner (Fig. 30), in the right hand, the collodion is poured upon it from the left hand, commencing at the corner 13. It is then allowed to flow by inclining the plate from left to right, and finally draining back into a separate bottle from the corner D, Fig. 31. If, at this moment, the plate be examined in a particular light, it will be seen that it is covered with an infinity of small ridges in the direction B D (Fig. 30); but on inclining the plate rapidly from left to right, these ridges will disappear. As soon as this happens, the plate is ready to be immersed in the nitrate of silver bath; but it is always advisable to wait a few seconds (and how many, experience alone can indicate precisely), so that the film may be sufficiently " set." There are certain characteristics by which it may be determined if the right moment has arrived for sensitising the plate; these are:
If the plate is immersed in the bath before the collodion has been allowed time to "set," the film will become detached in fragments; and, in this case, it will: be necessary to filter the bath.
If the immersion take place at the right time, the film whitens gradually.
If, on the other hand, the film be allowed to become too dry before immersion, it whitens instantly, and a good proof is never obtainable under these circumstances.
Fig. 31. Receiving the Collodion into a separate Bottle
Up to a certain point it is not difficult to determine when the plate should be immersed in the nitrate of silver bath. It will be found if the plate is looked at in a certain light, that it has assumed a dull, unpolished appearance. This, which is the right moment for immersion, will be arrived at in summer probably in about twenty seconds, while in winter it will probably take sixty seconds:
Apparatus for filtering Nitrate of Silver Bath.
Nitrate of silver bath is very easy to prepare. It is quite as well for those whose operations are conducted on a somewhat extensive sole to have a considerable quantity of bath solution, and keep it in a large bottle to which is adapted a funnel and filter, Fig. 32. The same filter will last a long time; and, on leaving work, the nitrate of silver bath which has been used during the day is poured into the filter, and in this way a solution in proper condition is always maintained at hand.
For the nitrate of silver bath, dishes in gutta-percha, porcelain, or wood with glass bottoms, are used, Figs. 33, 31, 37, Gutta-percha dishes are, perhaps, most frequently employed,2 but as vertical baths in glass and gutta-percha are also used, we shall say a few words in reference to them.
The reason why we recommend a gutta-percha dish in preference to one in porcelain is, that the film itself can be better seen, as also the impurities which float in the solution.
Figs. 33 and 34. Dishes in Porcelain and wood with Glass Bottom.
There are several methods of immersing the plates in the nitrate of silver bath; and as this is one of the most important points in the present chapter, we will pause to consider it somewhat in detail.
Fig. 37. Gutta-percha Dish.
Figs. 35, 36, 39. Dippers.
The dish containing the nitrate of silver bath being much larger than the plate, is raised at one end, Fig. 38, in order that the solution shall accumulate at the opposite 2nd; the plate, previously coated with collodion, is placed against the other edge, and held there by means of the finger or a silver wire hoop; lowering then the plate by a continuous motion, and allowing the dish at the same time to assume the horizontal position, the liquid flows at once, and without stopping, over the whole of the plate: after this the dish should be raised and lowered during a minute or so. Then introducing underneath the plate a hook made of flattened silver wire, Fig. 35, and by its means withdrawing the plate from the bath it will be seen to be covered by a number of veins which show that the nitrate of silver bath has not thoroughly penetrated the film, and that, there fore, the plate should be raised and lowered alternately until the silver solution flows evenly and smoothly over the whole surface of the film.
Figs, 40, 41. Vertical Glass Bath
It is at this point that the plate should be withdrawn, the fingers being covered with India-rubber finger-stalls, in the absence of which box-wood forceps, or an American clip, should be used, as the nitrate of silver blackens the hands very strongly.5 The plate is allowed to drain from the excess of adherent nitrate of silver solution, and is then placed in the camera frame. This method of operating requires only small quantity of nitrate of silver bath solution, which is accordingly exhausted in a proportionately shorter time. The plan we are about to describe requires, on the contrary, a large bulk of solution, which has the advantage of becoming very slowly exhausted. Moreover, a vessel may be used which is only just large enough to allow the plate to be immersed and withdrawn with freedom.
The solution is contained in a vertical bath, either of Mass or gutta-percha, Fig. 40; and by means of a hook or dipper of gutta-percha, which is introduced on the lower side of the vessel, the plate is immersed by one continuous motion into the fluid, raising and lowering it alternately as before. The plate is finally withdrawn ready for exposure, when the ridges or lines thereon have disappeared. In Note 6 are given details for the preparation of nitrate of silver bath.
Another plan we can much recommend is as follows:-Two silver hooks are first procured, made of flat sheet silver, and bifurcate, of the shape shown in Fig. 37. The nitrate of silver bath being contained in a dish (Fig. 42) of gutta-percha, the plate is held between the two hooks, the film being uppermost, and plunged at one strobe beneath the liquid, taking care at the same time that one end is immersed before the other, for unless this be done the liquid vein spin out of the dish. The plate being once fairly covered by the solution, one of the hooks is re moved; and with the other the plate is raised and lowered, in order to get rid of the veins or greasiness of which we have spoken above.
Instead of two books, it may be found more advantageous to use the two combined in one, as shown in Fig. 42. We may observe, in passing, that the silver hooks may be replaced by others made of whalebone.
In order to make these, it is necessary to hold them in the flame of a spirit-lamp until they bend, and to allow them to cool, maintaining pressure in the proper cure, by means of the fingers until quite cold.
Whichever method is followed in immersing the plate, in the nitrate of silver bath, it is indispensably necessary that it be the result of one steady and continuous motion for if this be not the case, lines will be formed upon the film, which will become apparent very soon in irreparable stains.
To preserve the hands from the action of nitrate o; silver, some amateurs use India-rubber finger-stalls, of gloves of the same material; but such apparatus will be found very inconvenient, and those who intend to be successful in photography should make up their minds before going into it, to sacrifice the delicacy of their hands and the whiteness of their shirt-cuffs.
We presume it is hardly necessary to observe that, at the time of sensitising the plate, the room should be made quite dark-an operation easily accomplished by moving the shutter in front of the yellow glass until the light is almost entirely excluded. With a little practice this will be found comparatively easy.
As soon as the plate is placed in the camera-back, the window and door may be opened, and the bath covered with a plate of glass, in order to preserve it from dust.
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