Platinum Chloride

Platinic - PtCl4.

Platinum Tetrachloride, Platinum Perchloride, or Platinic Chloride.

Brownish-red crystals. Soluble in water, alcohol and ether. Used chiefly in platinum toning.

Platinum Chloride

Platinum - PtCl2. Platinum Bichloride. Greyish-green to brown powder. Soluble in hot hydrochloric acid; insoluble in water. Used in making potassium chloro-platinite for the platinum process.

Platinum Toning

Collodion matt papers, after having been toned in a gold bath, are sometimes toned in a bath of platinum, which tends to make the image of a still more permanent nature. The platinum toning bath must first be acid, and second should contain a minimum quantity of a salt, for if the silver which constitutes the image is submitted to the action of an excess of salt, it is transformed into chloride without any metallic deposit being formed to replace it. For both of these reasons it is essential that the prints be very carefully rinsed after the gold toning and previous to entering the platinum bath.

Varnish for Platinum Prints

Although there are many formulae given for varnishing prints, there are very few that give the desired satisfactory results. The one which can be relied upon, however, is Adamantine varnish. A sufficient quantity of this varnish should be placed in a tray to permit of the whole print being dipped in it. All that is necessary is to immerse the print and then withdraw it, after which it should be hung up to dry.

Pneumatic Release

A rubber bulb and tube used for operating pneumatic shutters.

Pneumatic Shutter

(See Shutter, Pneumatic.)

Poisons

Some of the chemicals used in photography are poisonous either when taken internally or if absorbed through the skin or cuts. Complete table of poisons, with their effects and remedies, is given in the above reference.

P. O. P.

Printing-out Paper. Porcelain, Cement for.

Mix into a paste, then brush over the broken surfaces, pressing the latter into contact and drying in a warm place.

Porous

A term used when a substance has minute perforations, generally invisible to the naked eye, and through which fluids may pass.

Portrait Lens

(See Lens, Portrait.)

Rembrandt Portrait

(See Rembrandt Portrait.)

Portraiture

The art of making likenesses of individuals.

Positive

Opposite to a negative. The image of an object in which the lights and shades are represented as seen in nature; a plate or print which shows the picture correctly, and not reversed.