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The Carbro or Ozobrome Process 696

bath, carbon, water, print, bromide, gelatine and oz

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THE CARBRO OR OZOBROME PROCESS 696. Working Methods. In the Carbro or Ozobrome process,' invented in 1906 by T. Manly and improved by H. F. Farmer, in 1919, a carbon print is obtained from a bromide print, by single transfer, without reversal of the original bromide print' as regards right and left. The result is as good a.s a direct carbon print in all cases where critical sharpness is not required. After rinsing and re-developing the original image in ordinary light, it can be used again for making further carbon prints, up to a maximum of about ten copies.' The bromide print should be made on a paper with very hard gelatine. For this reason, semi-glossy papers, with their usually harder emulsions, are to be preferred to glossy Development must be carried as far as it will go. Fix in two baths, and wash very carefully.

The carbon tissue is cut to such a size that it projects at least a quarter of an inch beyond the bromide print on all sides. The latter having been previously trimmed, if necessary, is im. mersed for three minutes in Bath No. r below— (F. R. Newens, 1930).

Stock Solution No.

Potassium bromide . . 2 OZ. (Ioo grm.) Potassium ferricyanide . 2 oz. (Ioo grm.) Water, to make . . 20 OZ. (1,000 c.c.) Bath No. I ready for use Stock solution No. I . 20 c.c.

Water . . . 80 c.c.

The paper taken from Bath No. r is applied by its gelatine surface to a sheet of glass and blotted off. It is then placed in the second bath where it remains from 15 to 40 seconds, the shortest immersion giving contrasty images and the longest immersion soft ones.' Stock solution No. 2 POtaSSIUM bichroinate . 350 gr. (4o grin.) Chromic acid . 350 gr. (4o grm.) Chrome alum . . . 2 oz. (Loa grm.) Boiled water, to make . 20 oz. (z,000 c.c.) Bath No. 2 ready for use Stock solution No. 2 . 20 C.C.

Boiled water . . _ 2/ oz. 32 mm.

(So r A%) If the water used for diluting Bath No. 2 has not been freed by boiling from most of its lime salts, it would be necessary to increase slightly the amount of stock solution in this bath.

Bath No. I can be used a great number of tunes, provided it is occasionally filtered ; Bath No. 2, which is subject to continuous alteration by additions from the first bath, must be renewed frequently, at least once during each spell of print-making.

In the meantime, the bromide print, previ ously soaked in water until the gelatine is completely swelled, is placed face upwards on a sheet of glass.

The carbon tissue, on removal from bath No. 2, is laid with its gelatine surface against the silver image, leaving a uniform margin all round. Excess of liquid is rapidly removed with a squeegee, avoiding any shift of the two surfaces in contact (which may give rise to double images). The two papers are removed together from the glass, and left for a quarter of an hour between damp sheets of parchment paper (vegetable parchment). During this time a sheet of single transfer paper (§ 652), cut a little larger than the carbon tissue, is immersed in water for three to five minutes (according to its thickness). It is then placed on a sheet of glass, gelatine-coated face upwards. The bromide print, now bleached, is gently detached from the carbon tissue, and placed in water ; the carbon tissue is applied to the transfer paper, gelatine to gelatine, and contact obtained by pressure with a squeegee. The whole is left under pressure between damp blotting-paper. Washing off is then carried out (§ 654), in which, however, a temperature of 95° F. should not be exceeded, since the pigmented gelatine which is to form the final image is not rendered so completely insoluble as in the case of the direct carbon process.

The bromide print is washed in several changes of water, for at least 20 minutes, before being fully re-developed in ordinary light ; this re development may be postponed, the re-devel oped image being then washed without fixing.

Various formulae have been published for replacing the two successive baths Nos. i and 2 above-mentioned by a single bath, but these do not allow of so much control of contrast, and the prints successively obtained from the same silver image become more and more contrasty, the density of the shadows increasing whilst the details in the high-lights progressively disappear.

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