Various Methods of Development 381

oz, cc, developer, gr, water, grin, grm and negatives

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Acid A midol (Diaminophenol) Developer for Over-exposed Negatives (G. Balagny, 1912). Depth development (§ 361) is perfectly suited for very over-exposed negatives and for those of subjects with violent contrasts when it is wished to reduce these contrasts.' In this developer the image appears in about io to 15 minutes, the total time of development being usually not less than 2 hours, and lasting some times 12 hours. Development can, however, be conducted in a dish, as there is no deposit from this developer- :midol (diaminophenol hydrochloride) 90 gr. (so grm.) Sodium bisulphite lye 35' Be. .4 drm. (30 c.c.) Soda sulphite, anhydrous . . 50-70 gr. (6-8 grm.) Water, to make . . . 20 07.. ,000 C.C.) Developers Producing Negatives of Maximum Contrast. For obtaining the maximum of con trast, especially in the copying of drawings, printed matter, or manuscripts with black writing on white paper, it is usual to employ a hydroquinone and caustic alkali developer con taining a very large quantity of bromide. Such a developer can be obtained by mixing, at the moment of use, equal volumes of the following solutions A and B.

(A) Potassium metabisulphite oz. (20 grm.) Hvdroquinone . oz. (25 grm.) Potassium bromide . oz. (. grin.) Cold water, to make 20 oz. ( i,000 c.c.) (B) Caustic soda . oz. (5. grin.) Water, to make . zo oz. (1,000 c.c.) This developer can be used once only ; the average development time is 3 min. at 65 F.

It is often possible to obtain sufficient con trasts, though less considerable than with the above developer, by using the following solu tion, which is considerably cheaper, since it can be used repeatedly'— Metol 9 gr. (1 grin.) Soda sulphite, i oz. (75 gnu.) Hydroquinone . _ 8o gr. (9 grin.) Potassium carbonate oz. (25 grim) Potassium bromide . 45 gr. (5 grin.) Water, to make . 20 or. C.c.) Ultra-rapid Development. (H. Parker and J. I. Crabtree, 1936.) In photography and cine matography of topical events and for military intelligence work by aerial photography it is often necessary to cut down development time to a minimum (§ 382, footnote) without unduly sacrificing the quality of the images. This result is generally secured by using developers ren dered alkaline by a caustic alkali, or made moderately warm.

In either tank or dish, development cannot be uniform unless it lasts at least i min. ; on con tinuous machines this period may be reduced to 30 sec. in a case of absolute urgency_ Water, to make . . . or. ( E,000 c.c.) Nieto' gr_ (i4 grin.) Soda sulphite, anhydrous . oz. (5o grin.)

Hydroquinone . . gr. (1 grm.) Caustic soda . . . . 83 gr. (19 grin.) Potassium bromide . 30 gr. (9 grin.) The normal development time is about 2 min.

at F. ; it can be reduced to about x min. by using the developer at 86° F. (§ 391). To reduce these times by half on machines, the developer must have strong ammonia added to it at the rate of 12 mimims per ounce (25 c.c. per 1,000 c_c_)_ 389. Development in Several Successive Baths. This method, which is also called development in several dishes, usually employs two successive baths of different composition with, as extreme cases, the use of two baths of the same formula hut at different stages of exhaustion, and the use of pure water as the second bath.

We will deal successively with its application to the correction of variations in exposure, and to its trade use, where it is sometimes adopted for reasons of cost.

Correction of Variations in Exposure. This method of development is perfectly suited for supervised development of a large number of negatives taken in unknown conditions. De velopment is then begun in a dilute or slow acting bath, so as to retard the appearance of the image and to permit, after individual examination, of development being completed in a bath for under-exposed negatives, or in one for over-exposed negatives.

The different developers recommended by A. Hiibl (1897) are prepared from the same stock solution (or, rather, from a species of clear paste which must be well shaken before taking any for use), prepared as follows— Dissolve r oz. (25 grm.) of anhydrous soda sulphite in 21 oz. (70 c.c.) of hot water, and then / oz. (20 grm.) of glycin ; then add, in small quantities at a time (because of the effervescence which occurs in the mixture), 31 oz. (roo grm.) potassium carbonate. After the bubbling has ceased warm the mixture, if necessary, until all is dissolved, and then allow to cool. There should then be oz. (ISO c.c.) of a clear paste (if much less, from evaporation, make up the volume to this amount with water). Keep in a well-stoppered bottle.

In the trial bath, preferably cooled to 5o° F., development should be complete in 6o to 90 minutes ; with normally exposed negatives the image should appear in i5 to 30 minutes ; in such cases the development may be finished in the same bath or in a more concentrated developer.' Over- Under Treat exposed Exposed Belie Negatives Negataves Water, to make . . 20 OZ. 20 01. 20 07:.

(1,000 c.c.) (ices ex.) (r,000 c.c.) Concentrated developer . a Cr, z oz. e4 Cr. 44 Cr.

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