THE PEWTER PLATE.
The skin after exposure to light under the negative, etc., is mounted by means of a squeegee upon a plate of pewter 21 by 15 by 1⁄8 of an inch in thickness, and well polished. This plate is cleaned with benzole and coated with a solution of India-rubber in benzole (well filtered) and dried.
THE MASK.
To prevent the margin of paper upon which the ink picture is printed, being dirtied, it is necessary, after rolling up, to lay a mask over the skin, this mask having an opening in the centre the size of the picture. Paper suitable for this purpose is made by coating bank-post paper with a mixture of one part of gold size, and two parts boiled oil; this mixture is laid on the paper evenly with a sponge, then hung on a line to dry; when dry it is ready for use.
THE HELIOTYPE SKIN.
To prepare a skin 22 by 16, weigh out two ounces of a good gelatine, and soak it in ten ounces of cold water until soft, then place it in the porcelain {157} vessel of a “Bain Marie,” the outer vessel being duly provided with the requisite quantity of cold water; now place it over the fire or Bunsen burner, and stir until the gelatine is just melted, then add two drachms of glycerine; stir well, so as to mix thoroughly, and raise the temperature to 125° F.; add two ounces of solution No. 1, and two drachms of solution No. 2; stir well, then remove from the fire or Bunsen, and strain through muslin into a jug or beaker; now tie over the jug or beaker a clean piece of muslin, when the mixture is ready for pouring upon the ground side of thick plate glass, waxed, properly levelled, and slightly warmed. Begin by pouring in the centre of the plate, and gradually enlarge the circle until all the gelatinous mixture is out of the jug or beaker, then with a strip of clean card coax the gelatine to the edges.
Now examine the film for air bubbles, which, if present, must be removed, either by pricking with a quill toothpick, or by coaxing to the edge with a piece of card.
As soon as the mixture has thoroughly set (which it soon does), remove it to the drying box.
Of course, the requisite quantity of gelatine for more than one skin may be melted at once, but it will be better only to strain into the pourer, from the “Bain Marie,” sufficient for one plate at a time, remembering that the quantity now given is for one plate only; therefore, if two, three, four, or more plates are to be dried at once, the quantities given above must be increased accordingly.
The stock solutions named above are compounded as follows: