VARNISHING THE NEGATIVE; SENSITISING PAPER.
There is a double object in the varnish. The first is simply to protect the gelatine film from accidental abrasion. The second is to protect it from dampness. Dry gelatine has a great affinity for water, soaking it up readily. If ready sensitised paper is used there is little danger from damp, hut paper recently sensitised is some times put in the frames before it is absolutely dry, thus an unvarnished negative is likely to be spoiled.
A varnish particularly suitable for dry plates is now extensively sold. That known as Hubbard's will be found excellent.
A little skill is necessary to varnish plates properly, and possibly the first few attempts may result in failure. The plate to he varnished is warmed to a temperature of about 100° Fahr. This is a tempera ture which feels pleasantly warm to the hand. The plate is held with the film side upwards by the left hand bottom corner, and on it sufficient varnish is then poured to form a pool. This pool should cover about half the area of the plate. This latter is now gently "tipped," or sloped, so that the varnish will flow towards the corner opposite that by which the plate is held. The tipping must be very gentle, or the varnish will flow off the plate. When the varnish has reached the corner opposite the one by which the plate is held, the position is slightly altered so as to cause the varnish to flow to the left, and in that direction round to the corner by which the plate is held, and eventually to the corner immediately to the right of this. By this time the whole plate will be covered, but there will be on it far too much varnish. The bottle is brought under the last corner to which the varnish has flowed, and the plate is gently brought up to a vertical position. Whilst it is being so raised it is rocked in its own plane, other wise crapey lines will result. On the two lower edges there will now be a thick edge of varnish. This is re moved by running a piece of blotting-paper along each of these edges whilst the plate still retains the vertical position. For a few minutes the plate is now laid on one side to set. It should if possible be placed in a plate-rack with that corner downwards from which the varnish runs. It may, however, be laid against a wall standing on either of the edges next to this corner. In a minute or two the varnish will have set stiff, and it is only necessary to heat the plate once more when the process is complete. This time the temperature should
be raised considerably higher than before. About 150° Fahr., or quite as high a temperature as the hand can bear to touch for a second or so, will not be too high. The plate is now set on one side to cool.
The warming of the plate before varnishing, and the heating afterwards, may be performed either before an ordinary clear fire or over a gas burner, the plate being kept a few inches clear of the flame. Better perhaps than either of these is an Argand burner or a large paraffin lamp with a chimney.
The plate is ready to be printed from after it has become cool for the second time. The varnish should cover it in a perfectly even film, although even in the case of skilful operators there is at times found a line marking a thick edge along each of the edges next the corner from which the varnish was returned to the bottle. Such a slight defect as this is of no consequence, but as the beginner is likely to have much more serious faults it is well to know how the varnish may be re moved so as to go through the process a second time.
One of the flat dishes is thoroughly cleaned, and is warmed to about as high a temperature as can be con veniently borne by the hand. The plate from which we wish to remove the varnish is similarly warmed, and is placed in the dish film side upwards. Over it there is now poured sufficient methylated spirit to cover the film. It is allowed to remain so for a few seconds, the dish being rocked. A small piece of cotton wool or a camel's hair brush is now gently passed over the film under the surface of the warm spirit. The greater quantity of the varnish is thus removed, and if the desire be simply to varnish the film again it may be done at once. It is, however, sometimes required to remove the varnish very completely so as to enable, for example, intensification to be performed. In this case the plate is removed from the dish after what has been described is done, is warmed again to about the same temperature as before, and is held over the flat dish whilst some clear methylated spirit is poured over it.
The spirit which is now in the dish may be put into a separate bottle, to be used again for the same purpose if there be need of it.