This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
Manufacturers of plates usually number them according to their sensitiveness, although the number on a plate box is not always a guide to the quickness or slowness of the contents. A slow plate is usually numbered from 20 to 40, a medium from 45 to 50, and yet the Seed 27 plate is supposed to be as fast a plate as is made. This number is supposed to represent the sensitometer value but unfortunately makers of plates do not use the same sensitometer. As a general rule it will be advisable for the novice to start with a slow plate for landscape work. Of course, in photographing moving objects it is necessary to use a quick plate and a short expos-ure However, you must be your own judge and experience will teach you when to use a slow and when to use a quick plate. There are many good plates on the market and it matters but little which you may select, but above all things do not constantly change makes and grades of plates. Select a medium plate, say a Seed 26 and stick to it, at least for the first six months or until you know exactly what you can do and what you cannot do with it. Then it is time enough to try a slower or faster plate. Do not be in a hurry to change because some friend tells you of a "better plate." The following is a partial list of the well known plates on the market:
Seed Plates. These are made in sensitometer 23, 26, 26x, 27 and Non Halation.
Cramer Plates. These are known by name as the "Banner," "Crown," "Isochromatic," slow, medium and instantaneous, "Non-Halation," and "Contrast."
Stanley Plates. These are made in sensitometers 35 and 50.
Carbutt Plates. These plates are made in sensitometer 16, 23 and 27, in ordinary plates. The "Eclipse," in 27; "Medium Orthochromatic" in 23; "Junior" in 27; a slow plate, "B 16" and a "Non-Halation."
Hammer Plates. These are known as "Slow," "Fast," "Extra Fast," and "Aurora" or Non Halation.
Now that we understand something of the action of light, of the various colors which go to make it up, of the construction of a plate and its sensitiveness to certain colors, we will proceed to load our plate holders and take a practical lesson in the field.
We have learned that our plate is sensitive to white light and that therefore we cannot handle it in either daylight or artificial light. We have also learned that it is less sensitive to red than any other color and for this reason this color has been selected for the glass of dark room lamps. These lamps can now be purchased from the simplest and cheapest for use with a candle, to the finest grades using oil and electric light. The prices vary from forty cents up to three or four dollars, depending on their quality and finish. Fig. 8 illustrates a cheap type of lamp which will answer very well for the novice. This lamp will be found very convenient when traveling as it folds up into a very small space. The top and bottom can be removed and the sides fold in. A ruby-colored fabric takes the place of the ruby glass. We will not undertake to fit up a dark room until you fully understand the requirements and will there-fore choose a small room, with say one window, which we can make absolutely light-tight by drawing down the blind and tacking over it a heavy shawl or some opaque oilcloth or other fabric. Now select a small table and chair and place your ruby lamp to the left-hand side of the table and your box of plates to the right. Close the door of your room and see that no light leaks in at the top or bottom and if it does shut it out by means of some opaque fabric. Light the candle in your lamp and close it. When all light is shut out from the room, you are ready to proceed with the loading of your plate holder. Turn over your box of plates and you will see, by means of the ruby lamp, that a strip of paper has been pasted over the joint to exclude all light. Carefully insert your knife in the joint and cut the paper around the four sides of the box, when the cover can be easily removed. You will find another box inside the first one and this being opened, will reveal the plates to you. The different manufacturers pack their plates in different ways. Some plates are done up in black paper, six plates in a package and two packages in a box, while others put the twelve plates together and the box is provided with Haps of black paper which fold down from all four sides over the plates. We notice that the upper plate is placed with the film side down and the next one with the film side up. All plates are packed with their film sides next to each other. The film side is the dull side of the plate. Take a plate from the box and bring it close up to the lamp. One side appears to be plain glass which reflects the light readily, while the other appears to be covered with a pinkish wax and is dull in appearance. The dull side is the film side and the film is not really red or pink as it appears but is a creamy white and appears pink on account of the red light from your lamp. Hold this plate in your left hand and scratch the film side, near the edge, with the nail of the first finger of your right hand. Now reverse the plate and scratch the other side and you will see a marked difference, Close the eyes and take another plate from the box and by means of your finger nail try and see if you can tell the film from the glass side of your plate. Practice this several times so that you can feel quite sure that you could distinguish the film side without the aid of the ruby lamp. It is quite important that you be able to do this, as it may be necessary to load your plate holders in the dark some time. The plates are divided into sets of two, film sides together and each set is separated from the next by means of frames made of cardboard or by strips on the end, depending on the manufacturers.
Now let us examine our plate holders. The plate holder is a shallow box having a slide on each side and divided down the middle by a partition of black cardboard so that we can draw the slide from one side without exposing the plate on the other side to the light. Plate holders differ slightly, according to the manufacture of the camera but in general principle are all alike. In some the slides are made of black rubber, while in others they are made of heavy board resembling leather. In the latter style the board is usually black on one side and light on the other and in some styles the slides are lettered on the black side "Exposed." Those holders with black rubber slides have a draw piece at one end made of wood and on examination you will see that this wooden draw piece is light on one side and is painted black on the other. In other varities the rubber is lettered "Exposed" on one side. The object of thus marking or coloring the slides will appear later.