Mr. Mayall published a form of process, employed by M. Martin, which differs in no essential particular from those already described ; but as involving some niceties of manipulation, on which, the writer says, depends the perfection of his finished pictures, it is thought advisable to quote it.
The albumen of a fresh egg must be beaten into a snow-like mass with a bunch of quills, dropping into it ten drops of a saturated solution of iodide of potassium ; allow it to stand six hours in a place free from dust, and moderately warm,—say 60°.
A piece of hand-plate glass, eight inches by six, with the edges ground smooth, must be cleaned as follows : with a piece of cotton wool rub over both sides with concentrated nitric acid, then rinse well with water, and dry. Stick a wafer on that side which I will now call the back, to mark it; pounce upon the face a moderate quantity of fine tripoli, moistened with a few drops of a concentrated solution of carbonate of potash; then with a piece of cotton wool rub the surface briskly in circles for about five minutes ; then with dry tripoli; then with clean cotton to clear away all the dusty particles.
To the centre of the back stick a gutta percha ball, as a handle : strain the prepared albumen through clean linen ; pour it gently into the centre of the cleaned side of the glass, keep it moving until the surface is entirely covered, run it into the corners, and finally pour off any excess at the four corners; disengage the gutta percha handle, and place the glass on another slab, that has been levelled by a spirit level, in a place perfectly free from dust, and moderately warm. I will call this my iodo-albuminized glass ; it will keep for any length of time, and may be prepared in daylight.
To excite (a yellow shaded light only being used), dissolve 50 grains of nitrate of silver in 1 ounce of distilled water and 120 grains of strong acetic acid ; pour the whole of this solution into a cuvette, or shallow porcelain dish, a little larger than the glass plate; place one end of the iodo-albuminized glass in the solution; with a piece of quill support the upper end of the glass, and let it fall suddenly on to the solution, lifting it up and down for ten seconds; take it out and place it, face upwards, in another dish, half filled with distilled water; allow the water to pass over the surface twice ; take out the glass, rear it up to dry; it is ready for the camera, and will keep in this state ten days,—of course, shut up from daylight, in a moderately warm place, but never moist. The solution may be filtered into a black bottle, and will do again by now and then adding a few drops of acetic acid, and keeping it in the dark. Expose in the camera from four to ten minutes, according to the amount of light and the aperture of the lens. Suppose I say a lens of three inches diameter, sixteen in focus for parallel rays, a one inch diaphragm placed three inches in front of the lens (one of Ross's photographic lenses is just the thing), the exposure would be in good light about five minutes.
Develope as follows. Place the glass, face upwards, on a stand with adjusting screws to make it level; pour a concentrated solution of gallic acid over the surface; the image will be from half an hour to two hours in coming out. It is best to apply a gentle heat, not more than 10° above the temperature of the room, it being 60°. Should the image still be feeble, pour off the gallic acid, rinse the proof with water, and pour on to it equal quantities of aceto-nitrate of silver and gallic acid reduced one-half with water. The image will now quickly develope; arrest it in four or five minutes, wash it well in three waters, and fix with hyposulphite of soda as follows :—
Three drachms of hyposulphite of soda to one ounce of water. Allow the proof to remain in this solution until all the yellow iodide disappears, wash it well, rear up to dry, and it is finished.
" Success is sure to attend any one practising this method, provided the eggs are fresh and the glass is clean: if the glass is not clean, or the eggs are stale, the albumen will split off in fixing.
Wash all the vessels, as soon as done with, with nitric acid, and then with water. Every precaution should be used to avoid dust. The albumen of a duck's egg is more sensitive than that of a hen's; and from an experiment of to-day, I am almost certain that of a goose is more sensitive than either."— Athenœum, No. 1220.