2d

To 1 oz. of collodion add 2 grains of iodide of ammonium. This will give very beautiful gradation in the half-tones, but not so vigorous a picture as the first.

3d

In 8 drachms of pure alcohol dissolve perfectly 8 grains of iodide of ammonium or iodide of potassium, and 1/2 grain of iodide of silver; then add 24 drachms of collodion. The iodide of silver ought to be freshly made, or the resulting negative will be of inferior quality. The iodide of ammonium too ought to be newly made. This collodion is one of the most sensitive, but the half-tones produced by it are inferior.

4th

In 8 drachms of alcohol dissolve 8 grains of iodide of potassium, 4 of iodide of ammonium, and 1/2 grain of iodide of silver; then add 24 drachms of collodion. This forms a very sensitive medium.

5th

In 2 1/2 oz. of collodion, 5 drachms of alcohol and 5 minims of liquid ammonia, dissolve 14 grains of iodide of ammonium. This forms a very good collodion, very sensitive and colourless.

6th

In 2 drachms of alcohol dissolve 6 grains of iodide of potassium, and add 6 drachms of collodion.

We now come to the:

Method Of Operating

I employ nothing but water to clean the glass plate with, using plenty of it, and rubbing the glass with the hand till the water flows freely over the surface. It must be well dried and rubbed clean with a linen cloth which has been well washed without the use of soap. When the collodion comes away from the glass, it is almost always in consequence of the existence of grease or dirt, or of a little moisture upon the surface.

Pour the collodion upon the glass in the usual way, and almost immediately immerse it in the bath of nitrate of silver, 30 grains to the ounce of water, lifting it in and out of the solution to allow the ether to escape. When it assumes a bluish opal hue, it is ready for use. By adding a little alcohol to the solution, one part of alcohol to ten parts of water, and one part of nitrate of silver, the collodion is more speedily rendered sensitive, and the image produced is more vigorous.

It seems of some importance to immerse the glass in the nitrate bath, and to place it in the slide in the same direction as that in which the collodion was poured off the glass plate.

After the appearance of the opal hue, if the bath be an old one, the plate may be left in it for some time without injury; but if the bath be new, it must not be left longer than is necessary to excite, or the nitrate would attack the iodide of silver.

To obviate this, it is well in making a new bath to add 1 grain of iodide of silver to each ounce of the nitrate solution.

It is unnecessary to filter the bath, as it is often altered in its nature by passing through paper containing injurious chemical constituents. A little blotting-paper drawn over the surface will remove any particles of dust that may be floating upon it.

If the bath contain alcohol, it should, when not in use, be kept in a stoppered bottle.

The Development Of Image

To effect this the plate must be taken again into the room, and with care removed from the slide to the levelling stand.

It will be well also to caution the operator respecting the re-moval of the plate. Glass, as before observed, is a bad conductor of heat; therefore, if in taking it out we allow it to rest on the fingers at any one spot too long, that portion will be warmed through to the face, and as this is not done until the developing solution is ready to go over, the action will be more energetic at those parts than at others, and consequently destroy the evenness of the picture. We should, therefore, handle the plate with care, as if it already possessed too much heat to be comfortable to the fingers, and that we must therefore get it on the stand as soon as possible.

Having then got it there, we must next cover the face with the developing solution.

This should be made as follows:

Pyrogallic acid.....5 grains.

Distilled water..... 10 oz.

Glacial acetic acid . . . . 40 minims. Dissolve and filter.

Mr. Delamotte employs Pyrogallic acid.....9 grains.

Glacial acetic acid .... 2 drachms. Distilled water.....3 ounces.

Now, in developing a plate, the quantity of liquid taken must be in proportion to its size. A plate measuring 5 inches by 4 will require half an ounce; less may be used, but it is at the risk of stains; therefore we would recommend that half an ounce of the above be measured out into a perfectly clean measure, and to this from 8 to 12 drops of a 50 grain solution of nitrate of silver added.

Pour this quickly over the surface, taking care not to hold the measure too high, and not to pour all at one spot, but having taken the measure properly in the fingers, begin at one end, and carry the hand forward ; immediately blow upon the face of the plate, which has the effect not only of diffusing it over the surface, but causes the solution to combine more equally with the damp surface of the plate: it also has the effect of keeping any deposit that may form in motion, which, if allowed to settle, causes the picture to come out mottled. A piece of white paper may now be held under the plate, to observe the development of the picture; if the light of the room is adapted for viewing it in this manner, well; if not, a light must be held below, but in either case arrangements should be made to view the plate easily whilst under this operation, a successful result depending so much upon obtaining sufficient development without carrying it too far.

As soon as the necessary development has been obtained, the liquor must be poured off, and the surface washed with a little water, which is easily done by holding the plate over a dish and pouring water on it, taking care, both in this and a subsequent part of the process, to hold the plate horizontally, and not vertically, so as to prevent the coating being torn by the force and weight of the water.