Ordinary cleaned glass plates are used; but if the printing is to take place by contact with the negative, the glasses selected should be the flattest procurable. There is nothing novel in the method of coating the plates. A small quantity of albumen is poured on a plate, and is guided over it with a glass rod. The plan of drying the plates is probably new to most photographers. A common earthenware pan is half filled with dry earth or sand, and on this a couple of handfuls of lighted charcoal are laid, the plate being dried over this in the following manner. A piece of thin wire is twisted at each end into a loop, and bent in form of a bow; the coated plate is sup-ported by fitting 2 opposite corners into the 2 loops, coated side down, and the arrangement is suspended over the fire by a string held in the left hand, a whirling motion being given to the cord by the fingers of the right hand, which causes the plate to spin rapidly round; this throws off the surplus albumen, and the plate is evenly and quickly dried. The plate must not be overheated, or fine cracks will be visible all over the surface. The albnmenised plates will keep for any length of time. To Sensitise the Plate. - The operations of sensitising and developing must be conducted in a yellow light.
Silver nitrate .. .. .. 30 gr.
Glacial acetic acid .. .. 30 m.
Water........ 1 oz.
It is a carious fact that the acid, instead of slowing the plates, rather increases their sensitiveness. An immersion of 30 seconds in the bath is sufficient. A creamy film must not be expected, the plate appearing but little altered by the action of the bath. The plates are washed, to remove the free silver nitrate, and set up to dry. In this condition they will keep for several days.
A full exposure must be given in this process, or cold tones will result. As the plates are very slow, it is advisable to print the transparencies in a frame by contact, and not in the camera. An exposure of 6-8 minutes in the shade may be required, and the employment of an actinometer, as used in carbon printing, is recommended.
Development is performed by pouring the following solutions on the plate placed on a levelling stand, or in a glass dish, which plates do not require Tarnishing. The use of mercury has been objected to on the ground that it induces fading; but the plates are quite permanent if properly washed after fixing, and again after removal from the mercury solution.
Clean a glass plate well, and rub over it a little powdered talc or wax dissolved in ether. Coat with normal collodion, and dry. Dip your prints in warm gelatine solution which has been filtered; run the same gelatine solution over the collodionised plate, and apply the warm and wet print face downwards. Then the card, dipped in warm water, is well pressed on with a piece of thin waterproof. A stout squeegee or scraper of glass is useful to press out air-bubbles.