There are several methods by which photographs may be reproduced upon enamel. However, since they are rather difficult, we will explain only one method, and for the other processes will refer the student to Dr. Paul Liesegang’s treatise on photographing on enamel, porcelain, and glass, which is printed in German.

In the first place only the best quality of mirror glass should be used for the plates, as it is essential that they should be perfectly smooth and without blemishes. The glass should then be cut the same size as the negative plate which is to be used later. The glass plate must be made perfectly clean, which is best done by placing it in a mild sulphuric acid bath for about ten minutes and then washing it well with clean water. It should be dried with a clean cloth or tissue paper, after which it may be wrapped in clean dry tissue paper and kept in a dry place until needed.

Out of the many receipts for preparing the sensitive solution, we will give only the two most generally found satisfactory. These are as follows:

(1) Dissolve one-half ounce of ammonium bichromate in five ounces of clean water. In another glass dissolve one ounce of grape sugar and one ounce of gum arabic in five ounces of clean water. When the solutions are completely dissolved, they should be mixed together, stirred considerably, and filtered several times.

(2) Dissolve one-half ounce of Le Page’s best fish glue and two ounces of grape sugar in five ounces of clean water. In another glass dissolve one-half ounce of ammonium bichromate in five ounces of clean water. When both are perfectly dissolved, pour the two solutions together, and stir them well, after which the mixture should be filtered several times.

These solutions should be prepared in the dark room and should not be kept more than a day or two, as both light and time will destroy their power. They should be kept in the dark room in a glass-stoppered bottle.

The sensitive solution, however it may have been made, should be poured over the clean, dry glass plate already described, as soon as possible after it is made. This is done in exactly the same manner that photographers prepare wet plates. The waste solution running off the glass plate should be filtered and saved as it may be used again. This pouring must be done in the dark room and dust must be carefully avoided. The wet plates should now be dried on an iron frame covered with paper and heated from underneath by a small gas or alcohol lamp. They should not be heated hotter than the hand can comfortably bear. When they are perfectly dry, they should be left in the dark room in a dry, warm place, free from dust and should be used the same day.

The next step is to place the negative that is to be reproduced in a copying frame with the glass side out. It should be perfectly clean and free from dust. The sensitive plate is then put in the frame with the sensitive side towards the negative. Any friction between the plates must be avoided. This, of course, is done in the dark room. The plates are now exposed in the sunlight from half a minute to a minute. If exposed in the shade it will take from five to ten minutes. If the weather is very damp it is advisable to use a previously warmed sensitive plate and negative for exposure to the light, since damp weather injures the sensitiveness of the plate. Also it is well to avoid any sudden change of temperature during the exposure. In the winter it is best to make the exposure in a warm room having about the same temperature as the dark room.

After the exposure is finished, the copying frame should be carried to the dark room, where the next operation must take place. First, the exposed sensitive plate should be taken carefully out of the copying frame and placed on a piece of paper with the sensitive side upward. The picture will not as yet be discernible upon it. Now place a quantity of black or brown dry enamel paint on the plate and gently scatter this powder over it by means of a soft, clean, dry brush, which should be kept for this purpose only. Then brush the enamel powder back into its bottle. It is very essential that no dust shall get into it. After five or ten minutes repeat the powdering and so on two or three times until the picture is clearly developed.

If the sensitive plate has been underexposed, the picture will develop rather quickly at the first powdering. This will generally give blurred reproductions, and it is scarcely worth while to bother longer with that plate. The only thing to do is to make another exposure. With a well exposed plate, the picture should develop slowly, that is, not before the second or third powdering. If the weather has been exceedingly dry, it is advisable to breathe gently on the exposed sensitive plate before beginning the powdering. If, on the other hand, the weather has been damp, the plate should be warmed slightly before powdering.

When the picture shows clearly, brush all the surplus powder carefully from the plate, which is now ready to be treated with collodion. Add about twenty drops of castor oil to a pint of 2 per cent collodion solution and mix it thoroughly. This mixture, which must be free from air bubbles, should now be poured over the powdered plate. The waste collodion which runs off the plate is contaminated by traces of the enamel paint and cannot be used again. After the collodion has hardened, cut around the edges of the plate with a knife and then place the plate with the collodion side upward in a dish containing a weak solution of caustic potash (half an ounce of caustic potash dissolved in a quart of water). This solution will remove all the chromium which has served its purpose. Leave the plate in this solution until the first appearing yellow coloring has disappeared, and then place it with the collodion side upwards in a basin with slowly running water, which will in about an hour wash away all the chromium and potassium salts. The plate should then be placed in a dish of clean water to which a few drops of nitric acid have been added, not more than enough, however, to give the water a slight sour taste. The plate may remain over night in this solution without harm to the picture, although a couple of minutes will be found entirely sufficient if one is in a hurry.

Next, the plate should be placed in a large basin of clean water with the collodion side downwards. If the collodion film has previously been cut properly around the edges, it will soon separate from the plate, which may be removed, leaving the collodion film floating in the water.

Meanwhile, the enameled metal plate, which has been prepared exactly the same as is done for enamel painting, should be cleaned with a soda solution to free it from all grease. It should now be placed upon a wire support and carefully brought under the floating film which can be deposited gently on the enameled surface by means of a soft brush. The plate should then be taken slowly out of the water and the overlapping parts of the film should be turned under the edges of the plate, after which it should be put on a piece of white blotting paper to dry.

If any air bubbles appear under the film, they should be brushed very gently with a soft, wet brush towards the edge of the plate, where they will do no harm. If this does not prove successful, the bubbles may be opened with a needle, after which the air may be pressed out with a wad of soft paper.

When the plate with the collodion film on it is perfectly dry, the collodion should be removed by placing the plate in a dish of concentrated sulphuric acid. Within a few minutes the collodion will entirely dissolve. When this has taken place, a brownish ring will appear around the plate, whereupon the plate should be removed at once and put in a large basin of clean water. Finally, it should be submerged in a weak solution of ammonia (one ounce of ammonia to a quart of water), which will neutralize the last traces of the acid, after which it should be left on a piece of blotting paper to dry.

The picture may now be retouched just as photographers retouch ordinary photographs, only the same enamel paint should be used that was used in the powdering process. After the retouching, the plate may be fired in a muffle, just as is an ordinary enamel painting, and then covered with a layer of fondant. The finished photograph may, however, be painted with enamel paints if the enameler desires to make a colored photograph.