US2497875A

US2497875A - Direct positive photographs using aerial fogging developer

Info

Publication number: US2497875A
Application number: US780405A
Authority: US
Inventors: Fallesen George Earle
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1947-10-17
Filing date: 1947-10-17
Publication date: 1950-02-21
Anticipated expiration: 1967-02-21
Also published as: DE850383C

Description

Feb. 21, 1950 e. E. FALLESEN 2,497,875

DIRECT POSITIVE PHOTOGRAPHS USING AERIAL FOGGING DEVELOPER Filed Oct. 17,1947

LOG E 5% 3- f! "v v ILL ISA/3U GEORGE E .FALLESEN INVENTOR h. h. Pmm' A TTORNEYS I Patented Feb. 21, 1950 DIRECT POSITIVE PHOTOGRAPHS USING AERIAL FOGGING DEVELOPER George Earle Fallesen, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application October 17, 1947, Serial No. 780,405

3 Claims.

ticularly to a method of making direct positive photographs.

Direct positive effects may be produced by solarizing the developable latent image by overexposure, by using a second exposure to obtain the Sabattier or the Clayden effect or by redeveloping a developed negative image. Solarizable sensitized products require very intense exposures to obtain the desired direct positive photograph. The use of a second exposure has obvious disadvantages from the point of viewof practical technique. Redevelopment adds at least two operations to the usual and normal developing procedure.

It is therefore an object of the present invention to provide a novel method for obtaining direct positive photographs. A further object is to provide a method for obtaining direct positive photographs which does not require solarization, a second exposure or a redevelopment. A still further object is to provide a method for obtaining direct positive photographs which avoids the disadvantages of the prior art methods of obtaining such photographs. An additional object is to provide a method for obtaining direct positive photographs which does not require exof my invention is a gelatino-silver halide emulsion such as a silver bromide emulsion, a silver bromoiodide emulsion or a silver chloroiodide emulsion. It need not contain optical sensitizing dyes although certain sensitizing dyes may .be added to it for the purpose of inducing aerial The digestion should be carried out without the use of sulfur sensitizers. An emulsion of this type is that known as Burtons emulsion, described in Wall, Photographic Emulsions. 1929, pages 52 and 53. Burtons emulsion is made as follows:

A. Silver nitrate grams 100 Water "cubic centimeters 500 Ammoniarto form clear solution.

B. Potassium bromide "grams" 80 Potassium iodide cl0 50 Soft gelatin "do-.." 20

W Water cubic centimeters 1000 C. Dry gelatine grams 250 2 B is heated to C. and A, cold, added to B with constant shaking, digested for 20 minutes at 50 C., and allowed to cool slowly. C is added after being allowed to swell for 20 minutes in water, drained and melted. The emulsion is then set and washed.

An internal latent image emulsion, that is, one which forms the latent image mostly inside the silver halide grains, as described on pages 296 and 297 of Mees The Theory of the Photographic Process, 1942, is especially useful for the process of my invention.

Most of the internal latent image emulsions are silver bromo-iodide emulsions of high iodide content, preferably containing at least 10%-20% of iodide. Burtons emulsion is an emulsion of this type, having a silver iodide content of approximately 40% of the content of silver halide. It is not absolutely essential, however, for the emulsion to contain silver iodide.

An internal latent image emulsion made as described in Davey and Knott U. S. application .Serial No. 790,232 filed December 6, 1947, now

abandoned, may also be used according to my invention. This emulsion is prepared by first forming in the absence of ammonia and in one or more stages silver salt grains consisting at least partly of a silver salt which is more soluble in water than silver bromide, subsequently converting the grains to silver bromide or silver bromoiodide and if the silver iodide content of the emulsion is less than 6% calculated on the total silver halide, treating such grains with an iodine compound to bring the silver iodide up to at least 6%, ripening preferably in the absence of ammonia and then either washing out some of the soluble salts or washing out the whole of the soluble salts, followed by the addition of soluble salts such as soluble chloride or bromide. An example of an emulsion made in this way is as follows:

Solution No. l:

Inert gelatine 20 grams K01 20 grams at 40 0. Water 560 cubic centimeters solllltziili No. 2:

grams 0 Water 520 cubic centimeters} 45 soluiionrgl'o. 3:

gr 3 195 grams a Water. 520 cubic centimeters at 45 Solution N KBr-.- grams KL i. 40 grams at 45 0. Water 500 cubic centimeters of 10% solution of KCl (by weight), and then add water to make .3 litres.

An internal latent image type of silver halide emulsion may be defined as one which, when a test portion is exposed to a light intensity scale for a fixed time between /100 and 1 second, and developed for 4 minutes at 20 C. in the ordinary, surface developer (Example 1), exhibits a maximum density not greater than /5 the maximum density obtained when the same emulsion is equally exposed and developed for 3 minutes at 20 C. in an internal type developer (Example 2). Preferably the maximum density obtained with the surface developer is not greater than t; the maximum density obtained when the same emulsion is developed in the internal type developer. Stated conversely, an internal la tent image emulsion, when developed in an internal type developer (Example 2) exhibits a maximum density at least 5, and preferably at least 10, times the maximum density obtained when the same emulsion is exposed in the same way and developed in a surface developer (Example 1).

The developer used according to my invention should be one which produces oxidation fog or aerial fog. Such developers have been described by Dundon and Crabtree in American Photo,,- raphy, 1924, vol. 18, page 742. An example of such a developer is a, hydroquinone developer containing little or no sulfite, and is illustrated in Example 3.

My new process is based on the production of fog in the unexposed areas of the emulsion and the inhibition of development in the exposed areas. With the emulsions heretofore described and with developers referred to in the preceding paragraph, this action occurs in the following way. The emulsion is exposed in the usual manner and is developed in such a way that aerial fog is produced. The unexposed silver halide grains are thoroughly and ,efifectively .fogged; at the same time, the development in the areas containing the latent image is so restrained that a very low density is obtained in the area of greatest exposure. The inhibition of fogging in the regions containing a latent image is proportional to the exposure, the least density being obtained in the region of greatest exposure. In this Way, a reflection density of 0.02 has been measured on paper in the region of greatest exposure and a fog density of more than 1.5 has been measured in the regions of no exposure.

The aerial fog is produced according to my invention in various ways and may be accelerated or intensified by resorting to various expedients. The developer used should preferably have low sulfite content and should contain no silver halide solvent more powerful (as a silver halide solvent) than sulfite. developer having low sulfite concentration is especially adapted to the production of aerial fog. A developer of this type is illustrated in Example 3. Aerial fog may also be increased by bubbling air vigorously through the developer in such manner that the air comes frequently into contact with the emulsion surface of the photograph during development. Certain chemical agents such as copper sulfate incorporated either in the developer or in the emulsion itself may be used to produce or encourage the production of aerial fog. Hydrogen peroxide or certain dyes, such as methylene blue, increase aerial fog.

In addition to the use of a developing solution which produces aerial fog, the emulsion may As stated above, a hydroquinone' dition to it of certain compounds.

' U. S. Patents 1,846,301 and 2,058,406) may be incorporated in the emulsion. Other compounds such as the quaternary salt, benzothiazolemethiodide, also increase the susceptibility of the emulsion to aerial fog, as do silver iodide and potassium iodide.

Fogging agents containing labile sulfur are generally unsuitable for use according to my invention. The fogging action should produce developable surface latent image in the unexposed silver halide grains.

An ordinary, surface type developer, that is, one which develops an image only on the surface of the grains of an internal latent image emulsion, is the following:

EmampleI p-Hydroxyphenylglycine "grams" 10 Sodium carbonate (crystals) do Water to 1iters 1 Development time, 4 min. at 20 C.

An internal type developer, that is, one which develops an image inside the grains of an internal latent image emulsion, is the following:

Example 2 Hydroquinone grams l5 Monomethyl-p-aminophenol .sulfate do 15 Sodium sulfite (anhydrous) do .50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate (crystals) do- 20 Water to liters 1 Development time, 3 min. at 20 C.

Example 3 I-Iydroquinone grams- 22.5 Sodium sulfite do 30 Paraformaldehyde do 7.5 Potassium metabisulfite do 2.6 Boric acid, crystals do 7.5 Potassium bromide do 1.6 Water to make liters 1.0

The developer was agitated durin the development by bubbling air through it so that the air came in contact with the emulsion. The emulsion was then fixed in hypo and washed. The resulting sensitometric curve was measured and plotted as in the accompanying drawing, in which increasing exposures are plotted as ordinates and density is plotted as the abscissa. It is apparent that a positive image having suitable characteristics was obtained as indicated by the slope and position of the curve.

It will be evident to those skilled in the art that my process aifords a means for obtaining a direct positive photograph by a simple exposure and development technique and therefore avoids the necessity of high intensity exposures or a second exposure or redevelopment in order to obtain a direct positive image. Y Y

I claim:

1. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following internal type developer:

Grams Hydroquinone 15 Monomethyl-p-aminophenol sulfate 15 Anhydrous sodium sulfite 50 Potassium bromide Sodium hydroxide 25 Sodium thiosulfate 20 gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 liter and developing only the unexposed portion of said emulsion layer in an aerial fogging developer with access of oxygen.

2. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between /100 and 1 second and development for 3 minutes at 20 C. in the following internal type developer:

Grams Hydroquinone Monomethyl-p-aminophenol sulfate 15 Anhydrous sodium sulfite 50 Potassium bromide 10 Sodium hyd'pxide 25 Sodium thiosulfate Water to 1 liter gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I) Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 liter rendering only the unexposed silver halide grains of said layer developable in the following developing solution with access of oxygen:

Grams Hydroquinone 22.5 Sodium sulfite 30 p-Formaldehyde 7.5 Potassium metabisulfite 2.6 Boric acid (crystals) 7.5 Potassium bromide 1.6

Water to 1 liter 6 and developing said grains to metallic silver in the same solution in which they were rendered developable.

3. The method of obtaining a direct positive image in a silver halide emulsion layer, which comprises exposing to light rays to which the emulsion is sensitive, a silver halide emulsion layer a test portion of which upon exposure to a light intensity scale for a fixed time between and 1 second'and development for 3 minutes at 20 C. in the following internal type developer:

Grams Hydroquinone 15 Monomethyl-p-aminophenol sulfate 15 Anhydrous sodium sulfite 50 Potassium bromide 10 Sodium hydroxide 25 Sodium thiosulfate 20 Water to 1 liter gives a maximum density at least 5 times the maximum density obtained when the equally exposed silver halide emulsion is developed for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 liter and immediately immersing said layer in a develoninsolution o sub tantiallv t e following composition with air bubbling through it in contact with said emulsion:

Water to 1 liter to develop metallic silver in the unexposed portions of said layer.

GEORGE EARLE FALLESEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Crouse et al May 28, 1946 OTHER REFERENCES Wall, Photographic Emulsions, Publ. 1929 by Amer. Phot. Publ. 00., Boston, pages 52 and 53.

Clerc, Photography, Theory and Practice," Pub. 1937 by Sir Issac Pitman & Sons, Ltd., New York, page 229.

Number

Claims

1. THE METHOD OF OBTAINING A DIRECT POSITIVE IMAGE IN A SILVER HALIDE EMULSION LAYER, WHICH COMPRISES EXPOSING TO LIGHT RAYS TO WHICH THE EMULSION IS SENSITIVE, A SILVER HALIDE EMULSION LAYER A TEST PORTION OF WHICH UPON EXPOSURE TO A LIGHT INTENSITY SCALE FOR A FIXED TIME BETWEEN 1/100 AND 1 SECOND AND DEVELOPMENT FOR 3 MINUTES AT 20*C. IN THE FOLLOWING INTERNAL TYPE DEVELOPER: