Читать книгу Photo-engraving, Photo-etching and Photo-lithography in Line and Half-tone - W. T. Wilkinson - Страница 9

First purchase seven pounds of commercial sulphate of iron (copperas) and put this into a gallon jug, and fill it up with boiling water (clean); stir with a clean rod at short intervals for three or four hours, then allow to stand until the sediment settles, and the top portion of the solution is clear and bright; then decant as much as possible into a bottle or bottles, and label “Saturated Solution of Iron.” Then again fill up the jar with boiling water, stir until as much as possible is dissolved, so as to be ready by the time the stock in the bottle is exhausted, and repeat the process until all the crystals are dissolved; then wash out the jar, reject the residue, and begin again.

But bear in mind that, unless there are crystals left in the solution after each addition of hot water, it will not be saturated; therefore, before taking the solution into use, be sure there are undissolved crystals in the jar.

For use, take of

Saturated Solution of Iron	10	ounces.
Acetic Acid	4	ounces.
Water	70	ounces.
Alcohol	1 ounce to 5 as required.

In the above solution, the alcohol is added to enable the developer to readily assimilate with the sensitive film, and the quantity requisite varies with the age of the silver bath, or, to be more correct, with the quantity of plates sensitized therein. At first, little or no alcohol will be required, but after a number of plates have been sensitized the developer refuses to flow evenly, and seems disposed to run over the edges of the plate; this is a sign that more alcohol is required, and when more has been added the developer will flow evenly as before; but when 80 ounces of developer require over 4 ounces of alcohol to make it flow, it is a pretty sure sign that the bath wants remaking.

The developer is applied to the plate after exposure, from a straight-lipped cup, or glass measure, which should be kept for the exclusive use of this solution, as the mixture of any of the other solutions with it will at once counteract its working power. {18}

THE FIXING OR CLEARING SOLUTION.
Cyanide of Potassium	3	ounces.
Water	20	ounces.

This solution is highly poisonous, both in solution and vapor, so it ought to be kept in an upright holder, the plate being lowered into the solution on a dipper; keep the solution well covered up, so as to prevent evaporation as much as possible.

After being in use a short time this solution will become weak and should be strengthened by the addition in the evening of a lump or two of cyanide and then stirred up with the dipper in the morning; the negative must not be left in this solution too long or the density of the film will be impaired, but must be removed and well washed directly all the yellow iodide has been dissolved.