US1552791A - of bochester - Google Patents

Description

Patented Sept. s', 1925;

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CONTROLLED BEVERSAL PROCESS.

No Drawing. Application filed July 5,

To all whom it concern:

.Be it known that 1 JOHN G. CArsrArr, a subject of the Kin veloped silver salts which are then conf verted into. a positive image.

As usually practiced heretofore, this method had the disadvantage that very exact exposure and develo ment of the first image was required, so t at there would be left, after the removal of the negative silver image, an image in the undeveloped salt that would reproduce correctly the tones of the original subject. As it is generally exressed, there is no latitude in the exposure. oreover, slight inequalities in the emuls sion orvariations of the emulsion as a whole from the standard produce objectionably nonuniform positives.

Myinvention relates to a method of con-- trolling the final image to compensate for differences in the original exposure, and

consists in the step, after the first develo ment, of removin' such an amount of t e remaining undeve oped silver salt as will yield, after the second development, a final 40 image having the desired characteristics.

I will now outline the production of a print by a reversal process including my invention.

Step 1.The sensitive plate, film or paper,

g of Great Britain residing at Rochester,'1n the count of Monroe f step and all the succeeding was used, the

1923. Serial No. 849,738.

- Step 2.-The film, after a thorough washing, such as ten minutes in running water, is submitted to the may be the 'following:

' Potassium permanganate, 4% soL, 1 part; sulphuric, acld (20%), 1 part; water, 20 parts.

An alternative reversing bath is, potassium bichromate, 2 grams; sulfuric acid, concentrated, '2 00;; water to 1 liter. .This ones may be performed in ordinary light and this fact adds to the convenience of the process.

Step ii- The film is then submitted to a clearing bath capable of removing from the filmithe compounds or products formed in the reversing bath.

If the first mentioned rever'sin bath was used, the followi clearing bat is satisialcigry: Sodium blsulfite, 20 gm.; water to 1 r. g If the second mentioned reversing bath following clearing bath is preferable: Sodium sulfite, 100 gm; water to 1 liter.

Step 4.--The printing characteristics of the film are then determined. A skilled o erator, working under standardized conditions, can judge the image with sufiicient accuracy'by viewing it by substantially parallel light transmitted through it. Another metho of testing the film, particularly if it is motion picture film, is to redevelo a small re-exposed strip and judge from t at how much of the undeveloped salts should be removed.

Still another method, when motion picture film, is to cut off several 'Assreuoa ro EASTMAN xonnx I reversing bath.- This working with small stri s and to place them for different lengths 0 time in the h p0 bath to be mentioned in Step 5, and t en redevelo them and ,thus determine which gives t e best image.

I have used the value here and in the for the capability of duced. Ordinarily expression printing claims as an apt term the image to be re roa negatlve is use in printing upon a separate element; and in reverse processes in general the density of the negative determines inversely the density of the positive printed therefrom in the same emulsion. This printing value ma be considered as inherent in the negative silver image or in the residual sensitive salts since they are complementary.

I test or judgment arrived at in Step 4.

Step 5.-Thisfste is the mostimportant individual one of tlic process and the one to which my invention particularly relates. The film is now submitted to a plain hypo bath, preferably quite dilute. In practice I use the following: sodium thiosulfate, 9 grams; water to 1 liter.

The concentration of portant and does not afiect the result if the action is carried to the same point, buta weak bath being slower acting. gives more exact control. The film is left in this bath which dissolves out the silver salt, usually bromide, until there is left the slightest visible traces of bromide in the hlghest lights of the picture. Since this step is performed in the open light, the operator has opportunity to judge carefully. This judgment of the image is intended to supplement and verify the results of the When working on a commercial scale, for instance with motion picture film in a continuous process, reliance may be placed entirely on the results of Step 4, but .in vqorking with small cut films or plates'or short strips of film more opportunity for judging during Step 5-is presented.

When the dissolving of the silver salt image has been carried to a point, such that the remaining salt will yield. a. satisfactory print, the filmi'is removed from the hypo bath and thoroughly washed.

Step 6'.-The remaining silver salt is then developed or converted into the final image. This may be done in any of numerous ways, some of which will be mentioned.

If a sepia tone is desired, thebath comprises 1% aqueous solution of sodium sulphide. This converts the salts to silver sulphide.

A bath giving a blue black tone is, stannous chloride, 100 gms.; hydrochloric acid, sp. gr. 1.17, 10 00.; water, 1000 cc. This is a powerful chemical reducer, converting the salts into silver.

Ordinary photographic developers may be used, such, for instance, as the following: monomethyl paramidophenol sulfate, 23 gms; sodium sulfite, 500 gms; hydroquinone, 92 gms; sodium carbonate, 50 gms; potassium bromide, 10 gms; water,

10 liters.

The use of developer has the advantage that it gives a method of control of the contrast in the final image. It is obvious that numerous toning baths, chemical reducers, and developers can be used in'this step and that the final image can be modified, tinted or treated by any of the many processes known to photographers.

After such final development, toning or other process, the film. would be given such washing or other treatment as would be necessary or customary, and dried as usual,

this bath is not imthe details of this finishing step being in accordance with regular practice. It is to be understood that when, in the claims, I refer to developing an image at this stage, I intend to include any process by which a. permanent visible image is obtained from the residual silver salts.

It is obvious that this method provides a simple way of controlling the density of the final image rendering possible considerable latitude in the original exposure. It is performed largely in ordinary light and the baths used are those that are already familiar to photographic workers. The

process is particularly applicable to the treatment of motion picture films taken by amateurs, where there is' liable to be considerable variation in the original exposure, since it is possible to produce final prints of reasonably uniform quality on the original film, thus lowering the cost to the user.

Numerous variations in the process are possible and I contemplate as within the scope of my invention all such modifications and equivalents as fall within the terms of the appended claims.

Having thus described my invention, what I claim as new anddesire-to secure by Letters Patent is:

1. In a process of making photographic images by reversal in a light sensitive element containing silver salts, which process comprises the forming of a silver image in said element, the removal of the silver image leaving an image of silver salts, and the transformation of said silver salt image into a permanent visual image, the step of removing certain of said silver salts before the completion of the step of transformation.

2. In a process of making photographic images by reversal from a photographic ele ment containing an image in light sensitive salts, the step of submitting the element to a bath thatwill affect the light sensitive salts to render them non-developable in the emulsion, the extent of such submission being controlled in accordance with the printing value of the element, and then developing an image in said element from the unaffected salts.

3. In a process of making photographic images by reversal from a photographic element containing an image in light sensitive salts, the step of submitting the element to a bath that will remove the light sensitive salt, the extent of such submission being controlled in accordance with the printing value of the element, and then developing an image from such salts as remain.

4. In a process of making photographic images by reversal from a photographic element containing an image in light sensitive silver salts, the step of submitting the element to a bath containing sodium thiosulfate accordance with the printing value of the such salts as remain. I a 5. In a process ofvmaking photographic element and then developing an image from imagesby reversal from hotographic silver images in alight sensitive elementewh-ich process comprises the removal of the silver, from the elementflandrthen the development of the element, the steps prior to the completion of development, of determining the printing value of the element and of rendering the light sensitive element cap-able of' only incomplete development in accordance with such determination.

6. In a process of making photographic images by reversal from photographic silver images in an element containing developable silver salts, whicll'process comprisesthe removal of the silver from. the element and then the development of the salts, the steps prior to such development of determining the printing value of the element and of removing a portion of such salts in accordance with such determination.

I In a process of making photographic images by reversal from photographic silver images in an element containing developable silver salts, which process comprises the removal of the silver from the element and then the development ofthe salts, the steps prior to such development of determining the printing value of the element and of submitting itto a bath of sodium thiosulfate in accordance with such determination; I

Signed at Rochester, New York, this 29th day of June, 1923.

JOHN G. CAPSTAFF.