TRACING-PAPER. There are two kinds of tracing paper, viz., transparent, and black. Transparent tracing-paper is made by smearing the paper with boiled oil,. or magilp, or colourless dam mar resin dissolved in turpentine or benzole ; or better still, with Canada balsam diluted with turpentine. Black tracing-paper is made by saturating a piece of blotting paper with a mixture of lamp-black ground in honey ; or by rubbing a piece of sized paper with black-lead or black chalk. The tracing is first made upon the transparent paper in lead pencil, this is then laid upon the black paper, and that with its blackened side upon the paper which is to receive the final drawing. The lines on the tracing-paper are then gone over with a porcupine's quill, or other hard point, exerting a gentle pressure. A corresponding outline is thus obtained upon the paper beneath the black one. Sometimes blue paper is used instead of black ; this is made by substituting indigo or prussian blue for lampblack.
The transparent paper made with Canada balsam takes ink and water colours freely. A tracing-paper is made in France from raw flax, and is called " Papier Vegetale." TRANsFERRING. A collodion picture which is not too porous and powdery may be transferred from the glass plate, when wet after the final washing, in the following manner :— Lay a thick and wet piece of blotting paper upon the film in such a way as to cover the plate all but about a quarter of an inch at one end. Turn the narrow edging of film which is outside the blotting-paper over it by means of a penknife, and then, beginning at that end, raise the blotting-paper gently off the plate ; the film will come off with it. It may be permanently fixed to a sheet of dry gelatinized paper, by laying the blotting-paper bearing the film upon the gelatinized paper, pressing. the two into close contact, and letting them dry spontaneously, when the blotting-paper will come off, leaving the ffim attached to the gelatinized paper so strongly as to resist all attempts to remove it again by scratching or rubbing. The paper may then be waxed.
Collodion positives may be transferred from glass to glazed leather by damping both the film and the leather with alcohol, pressing the two into contact, and in a few minutes peeling off the leather, which brings the film with it, apparently so incorporated with the black glaze as to be incapable of being removed by scratching with the nail, 8r,c.
Collodion negatives may be transferred to gatta.percha in the following manner described by M. Leon Cassagne at a meeting of the French Photographic Society on June 19, 1857.
" It is generally known that at the Imperial Printing Office of Vienna, when a good collodion negative has been obtained on glass, it is the custom to transfer it by means of a double film of gelatine, and gutta-percha dissolved in chloroform. The process which I have adopted, and which has never been described in the Bulletin of the Society, consists in first dissolving— Pure g-utta-percha . . 1.92 grammes
Chloroform, or Benzole . . 31.09 „ or, Gutta-percha . 2.56 grammes Chloroform, or Benzole • . 31.10 „ " You perceive that the quantities are not invariable. There are cases in which it is necessary to vary them. I shall not enter into details ; the operator, in each particular case, will be able to decide for himself.
" When the negative on the glass is dry and in good condition, pour on the collodion side a coating of the above solution. Let it run slowly and uniformly, that it may have time to penetrate and unite with the collodion film. As soon as this coating is completely dry, strengthen it with a second, formed of the following sub stances : Gelatine of commerce, (very white) . 30 grammes. Filtered water, as much as the gela tine can absorb, until it has swelled to the utmost.
Isinglass . • 5 Alcohol . . 15 „ " Melt the gelatine in the water which it has absorbed, by plac ing the vessel containing it in hot water. Melt the isinglass in the same way in the alcohol. Mix by degrees, and with care ; stirring with a wooden spatula this species of varnish. Warm it with pre caution, that it may not be injured by too much heat. Hold the negative, the coating of gutta-percha upwards, before a clear fire, or over a spirit-lamp, until it is heated to 10 or 20° centigrade ; then pour over it immediately (removing it from the flame of the lamp), a gelatine, as thin as its density will allow. It is unnecessary to say that the gelatine must be warm and perfectly liquid at the time. Leave it for an instant to cool and dry, shel tered from dust, and you will be able to remove easily, by means of the steam from boiling water, the triple film of collodion, gutta percha, and gelatine. This operation, which is very easy, is per formed as soon as you see that the film is slightly softened by the steam, and you should then begin to remove it from the glass at the corner from which the excess of collodion was poured off when the plate was collodionized. It often happens that the film disengages itself at this corner of the glass. It is a good plan to facilitate the entire removal of the film with a thin blade of flexible polished horn, on which, with the help of fingers, you support the film, while you detach it •by degrees, either with, or without, the aid of a thin thread of water, running drop by drop from a tap, and which insinuates itself by degrees under the collodion, between it and the glass. As soon as the entire film is raised, flatten it between two pieces of glass, having good surfaces, and sufficiently thick to act by their own weight. The collodion used must have sufficient consistency, not so much however as to leave stria; or lines on the plate when dry.