This stage reached, plunge the plate into the bath, without letting the collodion get too much set; if the setting be prolonged, the .result is not so good. A "nitrate bath" means a solution of 30 gr. pure silver nitrate in 1 oz. pure water, sunned all the while it is not in actual use, and when used, rendered acid, in the proportion of 2 drops pure nitric acid to 1/2 gal. solution. The plate remains in this solution till the greasy marks disappear; it is then taken out at once, placed in a funnel to drain not less than 5 minutes, and is ready for the slide.

Arrange the copying camera in the studio so that the light which passes through the negative to be copied comes only through one of the side lights, and have no reflectors of any kind. Behind the negative, however, place a piece of finely - ground glass, which renders the light perfectly even. Use Dallmeyer's No. 2b lens. With this arrangement the exposure is for 5 to 20 seconds. If the enamel to be taken is of small size, have a mask on the negative, and block out all light except that actually needed, as this enables you to take 4 or 5 images side by side, by simply pushing the camera dark slide a little way each time. The slide is one that goes in sideways, and takes two C.D.V. pictures on one plate, side by side.

The exposure and development of the image are matters requiring the greatest care and attention, as on the complete success of the transparency the whole process turns. The developing solution is made as follows:-

In warm weather, this may be more dilute - say, as far as giving 20 oz. water to the same quantity of pyrogallic acid. Then, of course, more alcohol will be needed. This should be made 3 days before it is used, as it is too vigorous in its action at the first. On the other hand, it must not be kept too long, as then it deteriorates in the other direction. These are the characteristics in development which must be obtained in order to secure a good result. The image must develop very slowly; must attain the exact density required at the same moment that it attains the right amount of detail in the high lights; when examined by reflected light, it must not be "filled up" in the dark parts, or at least the " filling up " must only extend to a very few tones, and above the very darkest; when examined by reflected light, it should show, in fact, nearly all the drawing and shading of the subject; while, of course, when seen by transmitted light, it should show up with extreme perfection. Every detail must be there, with a fair amount of density; but heavy blacks are to be avoided.

To secure these conditions in perfection is to secure a first - class enamel, as all the rest is a matter of course. In actual practice, it is best to place the plate on a level stand during the last stage of development, right under the tap; a full stream can thus be turned on at the exact instant at which it is required to stop the action of the developer.

The plate must be well washed at this stage, and the fixing be done with potassium cyanide.' Use a weak solution, and carefully avoid pouring it upon the face or other delicate parts of the picture. The washing should be copious, and should follow as quickly as possible on the completion of the fixation.

When the washing is complete, break off a small piece of the film at one corner of the plate, and direct a thin stream of water from the tap on this corner, making it strike on the bare glass. The use of a camel - hair brush here will facilitate raising the edge of the collodion, so that a large jet of water can be got under the film; this being directed in the proper manner by tilting the plate, will effectually loosen the film from the glass. As soon as this is done, restore the plate to the horizontal position, and with a pointed stick, like a pen - holder, break away from around the picture as much film as can well be spared. Clear off the broken pieces with the finger, and give a slight extra rinse under the tap. This must be gently done, as the film is all loose now, and may slip off if you are not very careful. Get about 2 or 3 oz. of water on the plate, holding it quite level, then, bringing the whole over a large dish filled a couple of inches deep with water, lower one end gently into the water, when the film will slip off into the dish without the slightest injury. If protected from dust, the film may be left at this stage quite 24 hours without any injury or deterioration. The next stage is the toning.

To make up the toning bath just right is an important feature in the process. The procedure is as follows:- Get a 16-oz. bottle, half fill it with water, put it into a saucepan, also half - full of water, and set the whole arrangement on the fire, or over the gas, till the water in the saucepan comes to the boil. If the glass bottle does not crack under this trial, it may be used with safety. Place in the bottle 1/4 oz. iridium potassio - chloride, fill it up with cold water, and set it in the saucepan again; this time, however, do not boil the water in the saucepan, but place it where it will keep very hot; shake the bottle occasionally. Afterabout 1/2 hour, remove the bottle from the hot water, and place it aside to settle and cool; when quite cold it will be fit for use. This solution will remain good any length of time, and possibly even improves by keeping.

To make up the toning bath, proceed as follows :- Place 12 oz. pure water in a bottle; add to this 14 dr. of the iridium solution; shake it up well. Now add, a few drops at a time, and shaking well after each addition, 7 dr. of a solution of gold chloride (strength, 1 gr. to 1 dr.) The bath is then ready for immediate use, but is better after keeping. It keeps indefinitely.

It is particular to note in this place that the solution in the iridium bottle will have a nearly black sediment; this is simply undissolved chloride. When - all the clear solution has been used up, more water may be added, and this remainder used in the same manner as the first lot; but care must be taken that too much water is not added, as 1/4 oz. of the chloride will not make 2 16-oz. bottles full of the saturated solution, but only about 1 1/3 or 1 1/2.