第12章

Adhesive Paper.--Take gum arabic, four ounces, put it in a wide-mouthed bottle and pour on water about one-third above the gum. Add half ounce of isinglass, or fish glue, and a small piece of loaf sugar. Let all dissolve, and spread over French letter paper, with a brush or piece of sponge.

If once spreading is not enough, perform the same operation a second time.

Black Stain for Apparatus.--Dissolve gum shellac in alcohol, or procure shellac varnish at the druggists', stir in lampblack, and apply with a sponge or bit of rag. This will adhere to metal, as well as wood, and is used for the inside of camera, tubes, etc.

Sealing Wax for Bottles.--Melt together six parts rosin and one beeswax, and add a small quantity of lampblack; or, if red is preferable, add red lead. Common white wax is best, as most chemicals act less upon it.

When bottles containing bromine are to be sealed, it is well to grease the stopper. This, however, only when the bottle is in frequent use, for if it were to be sent by any conveyance it would be likely to fly out.

Rouge.--The method employed by Lord Ross is probably unsurpassed in the production of rouge. He has given his process as follows:

"I prepare the peroxide of iron by precipitation with water of ammonia, from a pure dilute solution of sulphate of iron;the precipitate is washed, pressed in a screw press till nearly dry, and exposed to a heat which in the dark appears a dull, low red.

The only points of importance are, that the sulphate of iron should be pure, that the water of ammonia should be decidedly in excess, and that the heat should not exceed that I have described.

The color will be a bright crimson inclining to yellow.

I have tried both potash and soda, pure, instead of water of ammonia, but after washing with some degree of care, a trace of the alkali still remained, and the peroxide was of an ochrey color, till overheated, and did not polish properly."Care should be observed to apply rouge in a dry state to the surface of the plate.

I would remark, that so far as my experience has gone, I consider good rouge fully equal to any other polishing, material for the last or finishing polishing; consequently Ishall not take up my space in enumerating any of the great variety that find few advocates.

Why Rouge is to be preferred.--"Because it burnishes better, and because it assists in fixing the layer of gold, rendering it less susceptible of being removed in scales when heated too much."Rotten Stone.--"Purchase the best ground rotten stone of the druggist, put a few ounces at a time in a wedgewood or porcelain mortar, with plenty of clean rain water.

This should have about forty drops of nitric acid to the quart.

Grind well, and after letting the mortar stand two minutes, pour into a third. After remaining undisturbed eight minutes, finally pour off into a fourth to settle. Rinse back the sediment in the second and third, and grind over with a new batch.

Repeat the operation till you have all in the fourth vessel.

Let this stand several hours, and pour off the water very carefully.

Set the deposit in the sun, or by a stove to dry.

When perfectly dry, pulverize, and it is ready for use.

With a little trouble you will obtain in this way a much better article than can generally be bought of dealers.

For the last washing, alcohol, or a mixture of alcohol and water, is preferable."Potassa Solution.--The use of a solution of potassa in the preparation of the plate was suggested in the early history of the Daguerreotype.

It was thought to possess some peculiar property for improving the tone of the impression. It is used for moistening the rotten stone in polishing the plate, and may be prepared by putting about an ounce and a half of alcohol in a close bottle, and add half a stick of caustic potash.

This will soon become of a deep red color. For use, fill your small bottle, having a quill in the cork, with alcohol, and add a few drops of the above, or enough to change it to a bright orange or saffron color.

A Substitute for the Hyposulphite Solution.--M. DAGUERRE recommends the use of a solution of salt water for removing the coating off the plate.

I found this of some service at one time during my travels.

My hyposulphite bottle got broke and its contents lost, so as only to leave enough for preparing gilding. I resorted to the use of salt solution, and found it to answer well. Make a saturated solution of salt in water.

First wash the plate with clear water; then immerse it in the saline solution, when it should be agitated, and the coating will soon disappear.

Another process with a salt solution of half the strength of the above is very interesting and effectual. The plate having been dipped into cold water, is placed in a solution of common salt, of moderate strength;it lies without being acted upon at all; but if it be now touched on one corner with a piece of zinc, which has been scraped bright, the yellow coat of iodine moves off like a wave and disappears.

It is a very pretty process. The zinc and silver forming together a voltaic pair, with the salt water intervening, oxidation of the zinc takes place, and the silver surface commences to evolve hydrogen gas;while this is in a nascent condition it decomposes the film of iodide of silver, giving rise to the production of hydriodic acid, which is very soluble in water, and hence instantly removed.

This process, therefore, differs from that with hyposulphite.

The latter acts by dissolving the iodide of silver, the former by decomposing it. It is necessary not to leave the zinc in contact too long, or it deposits stains, and in large plates the contact should be made at the four corners successively, to avoid this accident.

Gilding Solution.--To one pint of pure rain or distilled water add fifteen grains of pure chloride of gold, and to another pint add sixty grains of hyposulphite of soda.

When dissolved, pour the gold solution into the hyposulphite by small quantities, shaking well after each addition.