In this process we have this series of operations: First, the plate must be perfectly clean. That is essential. Any little spot upon it will form a nucleus which will spread over the surface of the plate. The plate is then coated with albumen and allowed to dry without heating. It is then flowed with this collodion, and in the collodion is put the chloride, iodide or bromide of silver, which you need. It is generally the chloride, iodide or bromide of silver. This collodion is afterwards dipped into a silver bath, and then we get the sensitized silver surface, very thin and perfectly transparent. It is then ready to go into the camera. It is put into the camera soaking wet with nitrate of silver. It is exposed and then developed with a solution of sulphate of iron with some acetic acid. After it is developed, the developer is washed off, fixed with hypophosphite of sodium, dried, varnished and we get the negative.

Now, the curious part about this wet plate process is that it is slow. The compounds are not very sensitive compared with the modern compounds. In the second place it is essential to use it wet. If you took the plate out of the silver bath where you sensitized it and washed off the nitrate of silver adhering to it and put the plate in the camera you would not get a picture. The silver nitrate is essential to the production of the picture. It acts in this way: Where the light has acted upon the sensitive silver compounds and you proceed to develop the picture, when you mix the sulphate of iron and pour the developer upon the plate, as the iron comes in contact with the nitrate of silver, with which the plate is wet, it produces metallic silver, which adheres to those parts of the picture which have been acted upon by the light. That seems to be the philosophy, because if you wash the nitrate off you cannot develop a picture upon such a plate.

Now, this process of photography revolutionized the daguerreotype, revolutionized photography and the daguerreotype became obsolete. I think it displaced the daguerreotype in three years. This process was such an advantage—collodion was such a nice substance to work with—that it revolutionized the photography of those days, and the daguerreotype fell out of existence.

Now, when you take into consideration the time that people had to sit for their pictures—five or six minutes—you can conceive how hard it was to keep still. They had such queer contrivances to keep the head straight, they screwed you up in various positions, and this was particularly exasperating where they had to take pictures requiring a good deal of time. Dr. Draper, who took some of these daguerreotypes, and who I believe was the first photographer of these pictures, desired to take a photo of his estimable lady. His studio was in the old University Building in Washington Square. I believe Mrs. Draper had to sit twenty minutes for that picture. In order to produce the best effect he had a tank made in the top of the laboratory so as to produce a blue light. Mrs. Draper was very patient while he was at work with this, and unfortunately, Dr. Colton tells me, the result was two pictures on the same plate. I should think it would. That was the first effort ever made to take the human face with the daguerreotype. Of course, with all that paraphernalia, with that slowness of action, anything that worked within a minute was considered wonderful, and that was practically what happened when Scott Archer discovered collodion.

This wet plate process continued from 1851 to 1871, about twenty years. I have the pleasure of showing you an amateur outfit for this process, used in 1860 to take to the Rocky Mountains (exhibiting it). That is an amateur outfit carried over the Rocky Mountains in 1860 to take pictures. Here is the old tank that carried the water. Here are some of the bottles of chemicals, and the way it was managed was this: This was hooked up, on the end of these sticks. This was the black cloth used as the developing room by the operator. Here is a little window with yellow glass to develop the pictures. The plates and bromide of silver was carried in these two boxes. That was carried on top of the mule and the boxes on the sides of the mule, so that he had a pretty good mule.

Now, to-day we do the same work with that apparatus (exhibiting apparently a Kodak), and a great deal better work it is.

In 1871 a more important revolution took place even than the wet plate process or the daguerreotype. Many efforts had been made to overcome the use of the wet plate—the plate wet with nitrate of silver, and some of the efforts were very successful but usually troublesome. The plate was kept moist in a variety of ways: by honey, by tea, by infusion of tea, by beer, by coffee, and a multitude of all the funniest concoctions you could think of, but the process was destined to fail.

In about 1870 it was conceived that you could make an emulsion of these peculiar compounds of silver—these sensitive silver compounds—that you could make an emulsion that you could pour upon the plate and produce a picture just when you pleased, and it was found that by mixing the chloride that produces the sensitive material in one portion of your collodion and putting nitrate of silver into another portion of the collodion, in certain proportions, you could produce a collodial emulsion. They had to be mixed in just exactly the right proportions, so as not to have an excess of nitrate of silver or an excess of bromide.

But that process failed and only lasted a few years; although I have here one of the plate holders used by such a process.