The Uranotype
This process, devised by J. Wothly, in 1864, did not receive from the photographers the attention it merits, as it is always the case when a process is patented, and can be replaced by another equally practical which is not. It gives pictures of a very good tone, which are quite permanent; we have some made in 1866, which are suffered no change whatever, they seem to have been printed from yesterday.
The first process given by Wothly does not appear to be complete. It has been well described by H. Cooper and a gentleman who signs by the initial letter X.
The process published in 1865 by Wothly is as follows: A sheet of paper is sized by brushing with a paste made of 24 parts of arrowroot in 500 parts of water, to which are added a few drops of a solution of citric or tartaric acid, then coated with a collodion consisting of 100 cubic centimeters of plain collodion, a few drops of oil of turpentine and 30 cubic centimeters of the following sensitizing solution:
| Nitrate of uranium | 30 to 90 parts |
| Chloride of platinum | 2 parts |
| Alcohol | 180 parts |
The time of exposure is about that required for paper prepared with silver chloride. The image is bluish-black but weak. After washing the print is immersed in a solution containing 0.5 parts of chloride of gold for 2,000 parts of distilled water, and then fixed in a bath of sulphocyanate of potassium, which tones the image blue-black.
It may happen that the proof is slightly tinted red. This arises from a small quantity of lime in the paper which forms uranate of calcium.
To prevent the proofs turning yellow, it should be washed in an exceedingly weak solution of acetic acid.
If, after exposure, the print is immersed, without it being washed, in the gold bath, the image becomes rose-red, but the whites remain pure. The effect is peculiar.
H. Cooper’s Process (1865)
| PREPARATION OF THE PAPER | |
|---|---|
| St. Vincent arrowroot | 200 grains |
| Boiling water | 10 ounces |
Crush the arrowroot to fine powder, then rub it to a paste with a little water, and let an assistant pour a few drams of boiling water while you keep stirring all the time; finally, let him add the rest of the boiling water, the operator still continuing the stirring. The paste is allowed to cool, and will be thicker when cold than when hot. Remove the upper portion entirely when quite cold, otherwise, if any left, it will give rise to streaks. The author insists upon the necessity of all these cares. Two sheets of paper are now placed side by side on a flat board, then the surface of the first is covered with the paste by means of a sponge, proceeding, before you leave it, all over the sheet in a horizontal direction; the second sheet is covered in a like manner. By the time the second sheet is pasted, the first one will be partially dry. The sponge is now drawn over each sheet, in succession, in a perpendicular direction in order to efface the streaks from the first sponging. If the paste drags in a slimy manner, it is too strong, and a fresh arrowroot must be prepared, because dilution only ends in failure. Why dry, the paper is rolled under moderate pressure, and when it lies smoothly the maximum pressure may be applied.
| PLAIN COLLODION. | |
|---|---|
| Alcohol | 12 ounces |
| Ether | 4 ounces |
| Pyroxyline | 80 grains |
| SENSITIVE COLLODION. | |
|---|---|
| Plain collodion | 1 ounce |
| Nitrate of uranium, pure | 30 grains |
| Nitrate or silver | 5 grains |
Add the uranium first, and as soon as it has dissolved all that it can, add a grain or two of soda, and when settled pour off the supernatant collodion and add the silver.14 To coat the paper with collodion, use a board with a handle beneath, such as is used by plasterers. On this place a sheet of paper, the edges being turned up about the sixteenth of an inch; this enables the whole of the sheet to be covered without spilling the collodion or allowing it to run on the back of the paper.
There is a marked difference in the appearance of the prints when they leave the pressure frame. Some samples of collodion cause the picture to print of a beautiful green, others of a rich brown, and some of a yellow or orange tint. The last take the longest of all to tone, and difficultly assume the tint of well toned silver prints,15 those printing to green or brown tone very rapidly.
After printing the pictures are placed in diluted sulphuric acid, 1 to 30 of water, until the high lights are perfectly clear and white; this takes from ten to fifteen minutes. After washing well under a stream of water, they are placed in the toning and fixing bath.
| TONING AND FIXING BATH. | |
|---|---|
| Sulphocyanide of ammonium | 1 ounce |
| Water | 12 ounces |
| Chloride of gold | 1 to 3 grains |
After removing from this bath, the prints are immersed for a few moments in water, and then rapidly washed.
| FORMULA FOR PREPARING THE PYROXYLINE | |
|---|---|
| Nitric acid, sp. gr. 1.30 | 12 fluid ounces |
| Sulphuric acid, sp. gr. 1.845 | 36 fluid ounces |
| Water | 8 fluid ounces |
| Temperature | 130 degrees Fahr. |
| Time of immersion | 15 minutes. |
X’s Process (1865). (Secrets of the Uranotype)
Preparation of the Uranium Compound.—Precipitate the nitrate of uranium from its solution by concentrated liquid ammonia. Let settle the precipitate, decant, and wash in several changes of water. Dissolve it by heat in pure nitric acid, taking care not to add an excess of acid. The ammonio-nitrate of uranium salt is then crystallized and dried. Mix a solution of 6 drams of this salt, dissolved in 3 drams of water, to a solution of 15 grains of silver in 30 minims of water, and crystallize. This salt is called ammonio-nitrate of uranium and silver.
| SENSITIZING SOLUTION. | |
|---|---|
| Ammonio nitrate salt | 3 drams |
| Alcohol | 8 drams |
| Distilled water | 15 drops |
| Nitric acid, pure | 1 drop |
Plain Collodion.—Dissolve in a small quantity of ether 1 dram of Canada balsam and 1 dram of castor oil, filter and let evaporate the solution to the consistency of oil.
Of this, add 10 minims to a collodion made of
| Alcohol | 10 ounces |
| Ether | 20 ounces |
| Pyroxyline | 220 grains |
| SENSITIVE COLLODION | |
|---|---|
| Plain collodion | 12 drams |
| Sensitizing solution | 6 drams |
| Nitric acid | 2 or more drops |
Keep this collodion in the dark, as it is quite sensitive.
| PREPARATION OF THE PAPER | |
|---|---|
| Arrowroot, pulverized | 1 ounce |
| Water | 32 ounces |
| Solution of acetate of lead | 10 drops |
Heat to 100 deg. Fahr. and then add four ounces of albumen. The paper is floated on this solution for five minutes and hung up to dry. The sizing may also be applied with a sponge in the manner often described.
The proofs should be slightly over-printed and, before toning and fixing, placed for about ten minutes in the following solution:
| Distilled water | 40 ounces |
| Acetic acid | 1 ounce |
| Hydrochloric acid | 1 ounce |
After washing in several changes of water, the proofs may be toned in any toning bath, and then fixed with sulphocyanide of potassium, washing afterwards in the usual manner.