Black-and-white sepia toning kit and method for its use

Details Black-and-white sepia toning kit and method for its use Black-and-white sepia toning kit and method for its use

2000-05-23

2001-07-17

Le, Hoa Van (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Color imaging process

Chromatic image produced from achromatic reproduction image

C430S432000

Reexamination Certificate

active

06261747

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an improved sepia image toning kit and to a method for its use to modify the images in black-and-white photographic silver halide positive or negative materials.
BACKGROUND OF THE INVENTION
Black-and-white photographic prints or images are obtained generally by imagewise exposure of black-and-white photographic silver halide positive materials. The latent image is then processed using the appropriate photochemicals to provide the appropriate development of the silver and desilvering (“fixing”) to remove unexposed silver.
Black-and-white photographic silver halide positive materials refers to those materials in which a positive black-and-white image can be obtained, including black-and-white reflective prints, black-and-white positive transparencies and black-and-white motion picture intermediate and print films. Negative materials refer to those materials in which a negative image is created that can then be used later to provide a positive viewing image. Such materials include black-and-white negative films and motion picture negative films.
“Toning” refers to a process wherein the normal neutral gray black-and-white image obtained in the conventional photochemical process to a stable form that is not oxidizable. In addition, the color of the image may be changed. In some toning processes, the metallic silver image obtained after development is converted to a silver sulfide image to produce what are commonly known as “sepia” prints that range in color from yellowish brown to a color approaching purple.
Sulfide toning methods may be either direct in which the silver image is converted at once into the silver sulfide image, or indirect in which two steps are required. Thus, the indirect method requires bleaching metallic silver to silver halide (such as silver bromide), and then converting the silver halide to silver sulfide.
One commonly used two-part sepia toning kit is available from Eastman Kodak Company as KODAK Sepia Toner Kit. The use of this kit provides rich, warm sepia images in many conventional imaged black-and-white photographic silver halide positive materials.
However, the color or tint of a sulfide-toned photographic material depends upon the sizes and structures of the silver halide grains used, as well as the compositions of those grains and the addenda used in modern black-and-white emulsions. In addition, the type of exposure and photographic processing (for example, the development step) of the imaged materials can have an effect on the eventual toned imaged. For example, compactness of the developed silver surface area or remaining emulsion addenda may promote an undesirable image.
Toned images may be identified as “cold” or “warm” depending upon where the toned image falls within the conventional CIE color scale using a* and b* values (Commission Internationale de l'Eclairage). A “cold” tone would be an image that is on the bluish side of neutral (that is negative b*), and a “warm” tone would be an image that is on the yellow or positive b* (and partly red or positive a*) side of neutral. Methods for obtaining “cold” toned images are described for example in U.S. Pat. No. 2,607,686 (Current), U.S. Pat. No. 5,037,727 (McLean) and U.S. Pat. No. 5,688,635 (Parker et al).
As black-and-white photographic silver halide positive materials have been redesigned in recent years, for example, to have different silver halide grain compositions and sizes, and other components have been added to the silver halide emulsions, the effect of conventional toning solutions has also changed. The conventional sepia toning compositions do not always provide the desired color shift, especially to the “warm” side of neutral. Moreover, the known toning compositions do not always provide the image stability that is desired. In other words, the black-and-white images may not be sufficiently stabilized using current toning products to provide long-term image quality (metallic silver could remain after toning that was not converted to a silver salt that may be susceptible to oxidation).
Thus, there is a need in the industry for an improved means for providing “warm” sepia toned images with a greater variety of silver halide photographic positive materials, and to provide images with improved stability.
SUMMARY OF THE INVENTION
The present invention provides an improved sepia toning kit comprising:
a) a silver bleaching composition comprising a hexacyanoferrate as a bleaching agent and halide ions, the molar ratio of hexacyanoferrate ions to halide ions being at least 2.25:1, and
b) a toning composition comprising a sulfur toning agent.
This invention also provides a method of providing a warm sepia toned image comprising contacting an imagewise exposed, developed and fixed black-and-white photographic silver halide positive or negative material with aqueous solutions of compositions a) and b) described above, with washing between the two steps.
The sepia toning kit of this invention can be used to provide stabilized “warm” sepia tones in positive black-and-white prints or other black-and-white positive or negative photographic materials after they have been imagewise exposed, developed and fixed using conventional processing methods. The desired warm sepia color or tint is possible in a greater variety of photographic materials despite their increased silver halide emulsion complexity because of the modifications in the Part A silver bleaching composition. In addition, because more silver bromide is available for conversion to silver salt using the toning composition, image stability is improved so that image quality lasts much longer.
These advantages have been achieved by using a modified silver bleaching composition in the sepia toning method. In this silver bleaching composition, the molar ratio of the hexacyanoferrate bleaching agent to the halide ions has been increased significantly to at least 2.25:1.
In the practice of the present invention, it is desired to provide “warm” sepia tones as defined by the conventional CIE lab scale wherein both a* and b* values are considered. The a* value is a measure of redness (positive a* value) or greenness (negative a* value) of an image, and the b* value is a measure of blueness (negative b* value) or yellowness (positive b* value) of the image. In the art, a positive b* value is indicative of a “warm” image tone, but the a* value also should be positive also in order to provide a warm “sepia” (brownish) image tone.
It is a primary advantage of this invention that use of the sepia toning kit of this invention provides images in which at least the b* values are changed more than +0.1 on the standard a*b* color scale when measuring an image density of 0.8. Preferably both a* and b* values are independently changed at least +0.1, preferably at least +0.7 and more preferably at least +1.0, at an image density of 0.8. These changes are determined in relation to the conventional a* and b* values obtained by toning the same photographic black-and-white paper using the conventional KODAK Sepia Toner kit and conditions (see Kodak Technical Bulletin G-23, “Toning KODAK Black-and-White Materials”, 1989, pages 11-12). This commercial toning kit has a Part A in which the hexacyanoferrate is present at 0.015 mol/l, and the molar ratio of hexacyanoferrate ions to bromide ions is about 0.36:1.
On an absolute scale, the present invention provides a sepia tone in the resulting image in, for example KODAK POLYMAX Fine Art F black-and-white paper, that has a b* value greater than 3 and preferably greater than 3.5, and an a* value greater than 2 and preferably greater than 2.5. The current KODAK Sepia Toner Kit would provide a b* value of 1 and an a* value of 1 in an image in the same paper.


REFERENCES:
patent: 2607686 (1952-08-01), Current
patent: 3515555 (1970-06-01), Fassbender
patent: 3928040 (1975-12-01), Shimamura et al.
patent: 4609616 (1986-09-01), Frank
patent: 4816384 (1989-03-01), Fruge et al.
patent: 4965177 (1990-10-01), McLaen
patent: 5037727 (1991-08-01), McLaen
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