Home >> Encyclopedic Dictionary Of Photography >> Formula to Or Film Negative Process >> Negative

Negative

plates, air, disk, dried and gelatine

NEGATIVE DRYER.— Many attempts have been made to devise a machine by which negatives may be dried in the shortest possible time. The most successful have been those which, by a centrifugal motion, create a strong current of air which takes away the moisture much sooner than by applying heat.

It is not generally understood that the drying of a negative has a great influence upon its character. If it is dried as quickly as possible the result is a pluckier negative richer in contrasts. Most amateurs make the mistake of placing the negative near some heating arrangement, often with the result that the film is softened or melted.

A better method than this is to stand the negative on the window sill with the window open, so as to have a free current of air passing over it. It will dry much sooner. The possibility, how ever, of the negative falling from the windowsill to the ground below is a decided disadvantage, and if one is located on the twenty-second story of a modern New York building the chances of its reaching the ground without injury are somewhat small.

The most suitable apparatus that we have noted for the studio or for those making a large number of negatives, is the one devised by Mr. F. M Pickard and described in the Revue Universelle.

The apparatus consists of a fin with wings, A ( Fig. 295), secured at the bottom of a vertical shaft B, given by gears and pinions D, D', D", D'', which are in turn operated by means of a crank, C, or by an electric or water motor, etc.

The plates to be dried to are inserted between two disks, E and E', loose on the shaft, and which are provided with grooves, H, H, to hold the plates. The upper disk, E', is adjustable verti cally, and can be secured by means of a screw, I, by which the disk may be secured to the shaft B. These vertical rods connect the disks, and serve to secure the coincidence of the groove

in the upper disks with those in the lower. Further a grooved flanged disk, M, which may be displaced circumferentially serves to lock the negatives in place.

To operate the apparatus the side, K, is swung back. The upper disk is raised sufficiently to allow the intro duction of the negative. The grooves in the disk, M, M', are then brought to such a position as to secure the nega tives. The negatives should be placed with the gelatine side away from the current of air produced by the fan. The side, K, is then closed. If now the thumb-screw, I, is not screwed up, only the fan is set in motion ; consequently the air, drawn in at the central opening in the back, will be forced violently against the walls of the cylinder and thrown back back by the cover at the upper end, under a current of air of this strength. The water contained in the gelatine films on the plate will be soon evaporated. When the gelatine is dry on the edges of the plates, the detach ing of the film from the plate is impossible, and the thumb screw, I, may be screwed up, the plates thus being revolved along with the fan, without danger that the film will be dis turbed. In a few minutes the plates are dry enough for printing by contact. A gelatine plate, developed and worked for twenty-four hours, may be dried sufficiently for printing by contact in fifteen minutes after being placed in the machine, if allowed to drain for a minute before being placed in the latter. The same machine may be used for drying plates, which have been varnished, or which have been immersed in an orthochromatizing solution