JPS5941878B2 - light sensitive material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to photographic materials, and more particularly to photographic stand materials.

Recently, it has been discovered that silver halide emulsions can be processed to form reflective optical data storage and laser recording surfaces. The present invention satisfies the need for a support material capable of recording information on both sides of a recording medium. Conventionally,
Double-sided laser recording and zeta storage media have been manufactured and disclosed.

However, most prior art media were formed by thin plastic discs, such as records. Co-pending U.S. Patent Application Serial Nos. 55,270, 72,9, all recently assigned to the assignee of this invention.
No. 08, No. 131,288 and No. 140,136 disclose the production of data storage and laser recording media consisting of silver halide emulsions.

In either case, reflective silver grains occur at the upper surface of the silver halide emulsion. In the manufacture of X-ray film, it is necessary to maximize the coverage of the emulsion on the substrate in order to capture the image produced by the X-rays. To accomplish this, it is often done to coat both sides of a transparent substrate with an X-ray sensitive silver halide emulsion, as described in US Pat. No. 4,130,438 to VanDOOrselar. Such emulsions are characterized by coarse silver halide grains, typically larger than 2 microns, so that low amounts of X-rays are absorbed to produce visible exposure. X
In line film, the substrate is usually made from a thin transparent plastic material so that the two emulsions are spaced relatively closely together so that the focus within the two emulsions can be maintained simultaneously. placed. This invention is not to be confused with stripping films in which the silver halide emulsion can be stripped from the substrate, such as U.S. Pat. No. 3,844,789. In stripping films, the emulsion coatings usually perform different functions. In this invention both emulsions adhere firmly to their supporting substrates and the two emulsion coatings are fine grained and perform similar functions. It is an object of this invention to provide a photographic mounting material suitable for forming double-sided laser recording and data storage media.

The above object is achieved with a light-sensitive platform material featuring a single substrate, which can be either transparent or opaque.

The substrate has parallel opposed substantially planar major surfaces that receive a fine-grained, light-sensitive silver halide emulsion. The fine grain size allows high dissolution of small spots that can be recorded in the emulsion before or after processing steps. This kind of processing. The emulsion is converted to a developed state in which its upper surface is reflective suitable for use as a reflective laser recording and data storage medium. Referring to FIG. 1a, the platform material 11 is shown in cross-section.

The glass substrate 13 has a main surface 15 located parallel to it.
and 17 are provided. These major surfaces should be substantially flat to define a focal plane in the emulsion on that major surface. The substrate 13 is 2m
It may be an optically clear glass having a thickness on the order of m. However, the thickness of the substrate is not critical. The substrate is coated on both sides with a fine grain silver halide emulsion of the type used to form photomasks for semiconductor integrated circuits.

One such emulsion is sold by Agfa Gevaert under the trademark 4'HD MillirTla8ki.

The composition of such fine grain emulsions is described in U.S. Pat. No. 4,004,925, column 6, 27-6.
It is explained in line 8 and column 7, lines 1 to 26. Other similar fine grain emulsions may also be used.
These emulsions are characterized by a grain size of less than 0.1 micron, preferably primarily less than 0.05 micron. The emulsion can be developed black and transparent even if light attenuating dyes or screening agents are used where the light exposure is made as opposed to chemical exposure with fogging agents such as, for example, borohydride. Head over. If light exposure is to be used, it is desirable to expose only one emulsion at a time. This means that
This is done by providing an opaque substrate or, if a transparent substrate is used, by providing a light-absorbing dye that immediately attenuates the light rays. Attenuation dyes are well known in the photographic industry. In this application, attenuating dyes are often used to absorb light rays that would otherwise pass through the substrate and activate the photosensitive silver halide on the other side of the substrate. Most light-sensitive silver halide emulsions are
Red attenuating dyes are preferred because they are sensitive to ultraviolet light and blue and green light. Additionally, attenuating dyes prevent halation caused by specular reflections at the emulsion and substrate interface. As mentioned above, the processing of silver halide emulsions is intended to provide reflective data storage and laser storage surface terminations to the substrate.

In some instances, it is desirable to pre-record information photographically on the emulsion before making it reflective. This means that
This is done by exposing the prerecorded information to light and conventional chemical development, thereby forming portions of the emulsion containing the prerecorded indicia. Photographic development of these areas produces black and clear areas that are depleted of silver and therefore unavailable to form a shiny reflective surface. Areas of the emulsion that do not contain prerecorded information are protected from light exposure, so the silver in these protected areas is used to form a shiny, reflective surface for data storage and laser recording. Emulsions 21 and 23 are applied to substrate 1 in a conventional manner, such as by the use of substitute layers.
3 so that the emulsion forms a sticky coating on the substrate.

The thickness of the emulsion layer is not critical, but thin layers are desirable, ie, in the range of 3 to 6 microns. The substitute layer is a very thin coating and is therefore not shown in the drawings. Emulsions 21 and 2
3 should have the same particle size.

The thicknesses of the two emulsions are preferably, but need not be, the same. The amount of silver halide in an emulsion is more important than its thickness, and the amounts of silver halide in the two emulsions are preferably the same. The emulsions may have a surface core layer prefabricated or activated by a fogging agent such as borohydride.

The silver precipitated cores produced are disclosed in U.S. Pat. No. 4,204,8 to Byers and others.
No. 69 and others. Nuclei can also be formed by exposure to light. Nuclei near the surface of the emulsion terminal with respect to the substrate are essential to form a reflective surface in one of the chemical processing methods described below. In these chemical methods, a silver diffusion transfer process is used to reduce the silver ions from the emulsion to nuclei and precipitate to produce non-filamentary silver particles. However, in other processing power methods, the completely unexposed portions of the emulsion are developed black and then heated to form a reflective surface. The embodiment of FIG. 1b is similar to FIG. 1a except that the substrate 33 is plastic rather than glass.

The plastic substrate may be any conventional photographic film stand material that is dimensionally stable. Most common photographic film bases are polyester, polyterephthalate, polycarbonate or cellulose triacetate. These film-based materials are usually optically clear, although opaque plastics may also be used. Referring to FIG. 2, a glass substrate 13' is shown in plan view.

The substrate illustrated in the figures is adapted for use as a disk medium. For this application, the dashed line 4
A rectangular glass plate designated by 1 is cut into an annular shape with an outer circumferential edge 43 and an inner circumferential edge 44 . The size of the annular disk can be any size desired for laser recording. Typically, the size ranges from a few centimeters in disc diameter to about 50? diameter range. The exact size is not important. →The T-blast may be converted into an annular shape as shown by solid lines 43 and 44 before or after coating. When a rectangular plate is coated on both sides with emulsion, it is done in one or two successive steps.

Coating of highly soluble emulsions may be carried out in a sodium beam chamber. Fog due to actinic radiation is somewhat less important for emulsion photomask materials. A perforated base through the glass prior to emulsion coating makes the board easier to handle during the subsequent operation of converting it into a disk. The substrate 13/ is placed on the pedestal 45 for coating.

Mounting platform 45 has a lower edge 47 that supports the underside of the substrate during the coating process. 48a, 48b,
Clear or opaque corner support materials, shown as 48c and 48d, fill the space between disks 13/and flush with disk 13' to provide a uniform edge and top surface for the emulsion coating bath.

Top surface and corner material 48a of substrate 13/
, 48b, 48c and 48d project slightly above the vertical wall of the pedestal. In operation, the pedestal is placed on a belt that passes under the shaped tank with a small opening at the bottom of the tank. A slight drop forms at the opening and is brought into contact with the substrate 13/, so that the drop either directly wets the substrate or is conventionally applied to the substrate for the purpose of fixing the emulsion. Wet the substitute that has been adapted. As the mounting passes through the bath, a thin layer of emulsion is applied to the upper major surface of the substrate. This step is the second
may be repeated to coat the emulsion layers. This mounting allows the coating of the glass disk without subsequent scraping and cracking of the glass which can scatter small glass pieces into the emulsion. Referring to FIG. 4, a two-sided silver halide emulsion 51 has a first emulsion coating 53 on one side and a second silver halide emulsion coating 55 on the other side. shown.

The coating of FIG. 4 is similar to the silver halide emulsion coating described with reference to FIGS. 1a and 1b. In FIG. 4, substrate 57 is formed by joining two separate substrate members 63 and 65 together for permanent contact. Such a bond may be made by epoxy. A red dye may be incorporated into the epoxy to filter any light transmitted through the silver halide, rather than adding dye to the silver halide itself. There should be no reflections from the bonding layer to avoid halation. Bonding should be achieved in such a way that the reflective exposed surfaces of the substrates are parallel to each other. The substrate material (should have a flat surface on the main surface. Ag on a thin glass substrate)
Currently available unexposed photoplates, such as fa-Gevaert HD Millmask material, may be affixed back-to-back at any time to form the article of FIG. In other words, in the article of FIG. 4, silver halide emulsion 53 is applied to substrate 63 before the two substrates 63 and 65 are bonded together in bonding layer 67, and Silver halide emulsion 55 may be matched to substrate 65. Care must be taken when processing these emulsions to maintain the top surface of the silver halide emulsion in a flat parallel plane. Although the use of two thin substrate members is illustrated with reference to FIG. 4, the use of more than one thin substrate member may be used, particularly if beneficial optical or mechanical properties for the substrate result. It is not excluded.

The materials of this invention are used to form two-sided reflective laser recording media.

A silver halide processing process is illustrated with reference to the following example. Example A United States Patent Application Serial No. 131,
In No. 280, a laser recording medium is provided by heating a substrate coated with a silver halide emulsion that has been previously exposed to light and developed black.

Heating is continued until a reflective surface appears on the surface of the emulsion. The substrate is transparent or absorbent and can withstand temperatures of at least 280°C to 340°C without thermal distortion. Prerecorded database and control information can be applied photographically to the media prior to black development.

The complete medium is then exposed to actinic radiation or a fogging agent and developed to form a black surface on the emulsion. This is followed by heating the recording medium in air or oxygen at about 270° C. to 340° C. until a shiny reflective component appears on the top surface. The gelatin in the emulsion is partially pyrolyzed, increasing its absorbability and therefore requiring less laser power. Example B In United States Patent Application Serial No. 72,908, a reflective data recording medium is formed from a silver halide emulsion in three steps.

First, a substrate coated with a silver halide emulsion is exposed to actinic radiation or treated with a fogging agent such as hydrazine or potassium borohydride to form silver precipitation nuclei. Alternatively, such a core layer may be included in the original manufacture of the silver halide photographic plate or film. Second, the exposed or activated film develops a surface latent image and forms soluble complexed silver ions and, by silver diffusion transfer, forms a reflective silver image. The silver is precipitated and contacted with a bath solution to form ions in the layer containing the nuclei or the nuclei of the latent image during development which are reduced. The silver diffusion transfer process is described below with reference to Example C. The only difference between this example and Example C is the following annealing step. Third, the resulting reflective silver image is thermally annealed at about 250°C to 360°C, preferably in an oxygen atmosphere;
Increasing the reflective layer and decreasing the gelatin layer increases gelatin absorption, thereby resulting in higher laser recording sensitivity.

The heating methods include air convection ovens, heat source contact or radiant heating. Photographic plate substrates can be either transparent or absorbent, but must withstand the temperatures used in the thermal annealing step.

Prerecorded data and control indicia may be adapted by photographic techniques prior to the processing described above. Example C In United States Patent Application Serial No. 55,270, a reflective data storage medium is formed by silver diffusion transfer similar to the process used in Serial No. 72,908 without a thermal annealing step.

The substrate can be a common photographic film base such as polyester, polyterephthalate, polycarbonate or cellulose triacetate. This is because no heat treatment is used. The substrate can be either transparent or absorptive depending on the wavelength of the recording or reading beam used. A coating of silver halide emulsion is applied to the substrate. Fine-grained silver emulsions are preferred for laser recording materials because they allow recording and reading of smaller holes. The surface latent image may be formed by exposure of the emulsion to actinic radiation or by a fogging agent, or alternatively a layer of silver precipitation nuclei may be included near the emulsion surface during the manufacturing process. Silver Diffusion Transfer Process for Forming Reflective Surfaces from Silver Halide Emulsions A very thin highly reflective silver surface is formed by diffusion transfer of suitable complexed silver ions to a silver precipitate nucleation layer.

This reflective layer is electrically non-conductive and has low thermal conductivity, and may be photographically patterned, these latter two properties being highly desirable in laser recording media. Complexed silver ions are formed by reaction of appropriate chemicals with the silver halide used in conventional silver halide emulsions. A developing or reducing agent must be included in this solution so that complexed silver ions can be precipitated into the core layer. The combination of developer and complexing silver solvent in one solution is referred to as a one-bath solution. Preferred one-bath agents for highly reflective surfaces include developers that may be characterized as having low activity. The particular type of developer selected is believed to be less important than the activity level, which is determined by developer concentration and pH. The developer should have sufficient redox potential to cause ring formation and absorption or agglomeration of silver ions at the silver nucleus.

The concentration of the developer and the pH of the bath solution should not cause the growth of filamentary silver giving a dark, low reflective appearance. The developed silver particles should have a geometric shape, such as spherical or hexagonal, which when aggregated forms a good reflective surface. Developers with favorable properties are well known to those skilled in the art, and most photographic developers require the concentration, pH, and silver complexing agent to be selected such that no chemical reaction occurs between the developer and the complexing agent. The effect can be produced by

It is well known that photographic developers require antioxidants for their protection. The following developer/antioxidant combinations were prepared using exposed and monobath developed Agfa-Geva
Typical reflectances were produced for the ert"HD Millimaskl" photographic plate as shown. Na(
SCN) and NH as a monobath solution solvent using a silver complexing agent.
Preferred solvents/silver complexing agents that must be compatible with a one-bath developer using 4OH and a silver complexing agent are mixed in proportions that promote complete diffusion transfer processing within a fairly short period of time, such as a few minutes. Ru.

Such silver complexing agents at practical volume concentrations should be capable of decomposing essentially all of the silver halide in a fine grain emulsion within only a few minutes. The solvent should not react with the developing silver particles to decompose them or to form silver sulfide because of their tendency to form non-reflective silver. The solvent should be such that the specific rate of reduction of the silver complex in the silver core layer is sufficiently rapid even in low activity developer solutions. The low activity developer is preferred to avoid the formation of low reflectance black filamentary silver in the initial development of the surface latent image. The chemicals listed below act as silver halide solvents and silver complexing agents in solution physical development.

They are grouped approximately according to the rate of solution physical development, ie the amount of silver deposited per unit time in the precipitated nuclei when a p-methylaminophenol-ascorbic acid developer is used. Highly active thiocyanate (ammonium, potassium, sodium, etc.) Thiosulfate (ammonium, potassium, sodium, etc.) Ammonium hydroxide Medium activity α Pyricone monoβ Bromide Phenylethylethylenediamine 2-aminophenolfuran n-Butylamine 2-amino Phenol Thiophene Isopropylamine Low Active Sulfate Hydroxylamine Potassium Chloride Potassium Bromide Triethylamine Sodium Sulfite From the above it will be appreciated that thiocyanate and ammonium hydroxide are among the most active solvents/complexing agents.

Although almost any developer suitable for solution physical development can be acted upon in the silver diffusion transfer process of this invention at a suitable concentration and pH, any solvent/complexing agent can be used within the desired short development time or in a suitable manner. It does not necessarily work in
For example, thiosulfate, i.e. in photography and P
The most common silver halide solvents used in the OlarOid-Land black and white instant photography diffusion transfer process do not work in this process for two reasons. The complexed silver ion is very stable, so it requires a strong reducing agent to precipitate the silver into the core, and the strong reducing and developing agent develops black filamentary silver with low reflectivity. This would have the undesirable effect of
It also has another undesirable effect exhibited by the thiourea solvent, namely that it forms black, low reflectance silver sulfide with the silver particles during its development. Other power,
In the black and white POlarOid-Land process, black silver is the desired result. Sodium cyanide is not recommended even though it is an excellent silver halide solvent. This is because it is an excellent solvent for metallic silver and therefore corrodes the image being formed. Although it is a common photographic reagent, it is approximately 50 times more toxic than sodium thiocyanate. Processing chemicals can be adapted in a variety of ways, such as by immersion methods, doctor blades, capillary applicators, spin spray processors, and the like.

The amount of processing chemicals and their temperature should be controlled to control reflectance. Preferably, the molecular weight of the developer is 7% or less of the molecular weight of the solvent. Because higher concentrations of developer lead to filamentary silver growth with low reflectivity, except for this ratio found between p-phenylenediamine and its N-dialkyl derivatives, PHII. 170mV to 24 at O
This is because it has a half-wave potential of between 0 mV and has a lower development ratio, requiring higher densities, ie, a maximum of 159 and a minimum of about 29 per liter. These derivatives and half-wave potentials are called “TheTheOryOfth
ePhOtgraphicPrOcess, 3rdcd
Macllan Company (1966)″″
They are listed in Table 13.4 of the book titled. The concentration of the solvent in the formation of soluble thiocyanate or ammonium hydroxide should be greater than or equal to 10 grams per litre, but less than or equal to 45 grams. If the concentration is too low, the solvent will not be able to convert the halide into a silver complex within a short processing time, and if the solvent concentration is too high, the latent image will not be sufficiently developed into the required silver precipitate nuclei. most of the silver complex remains in solution rather than being precipitated. The process in which the silver complex is cyclized with silver precipitated nuclei and forms the size of the nuclei is called solution physical development. In the solution physical development used here,
The silver particles do not form filamentary silver as in direct or chemical development, but instead grow more or less homogeneously in all directions, resulting in a developed image consisting of dense spherical particles. It is important to note that this happens.

As the particles grow, a change to a hexagonal shape is often observed. If the emulsion being developed has a high density of silver cores as grown, and if there is enough silver halide material to be dissolved, eventually the spherical shape will vary from some to several. will grow until it touches other spheres forming a collection of spheres or hexagons. As this process occurs, a ray of light conducted through this medium is
Initially, when the particles are very fine, they have a yellow appearance. This means that as the particle grows in size,
It will change to a red appearance and eventually exhibit a metallic reflectance when the aggregate forms. In summary, silver precipitation nuclei are formed on one of the surfaces of a silver halide emulsion by actinic radiation or fogging agents during the emulsion manufacturing process.

And if this emulsion is developed in a one-bath solution containing a weak developer and a very fast solvent that forms complexed silver ions that are easily precipitated by the catalytic action of the silver nuclei, and if the solvent If not, then a reflective coating is developed on one of the emulsion surfaces, thereby forming a medium for data storage and laser recording. While any common developer is effective, only a few solvents/complexing agents have all of the desired properties, and the most successful of these are soluble thiocyanates and water. It is ammonium oxide. In the common black and white silver diffusion transfer process, the silver in the silver halide, which is not used in the negative image, is removed from the silver halide containing precipitation nuclei to reduce the silver and thereby form the positive image. Diffusion into two separable layers.

In a diffusion transfer process, a volume concentration of silver precipitation nuclei may be formed at the emulsion surface without the use of a separate layer containing the nuclei. When activating radiation or fogging chemicals are used to form these nuclei in the data storage areas, the desired reflective layer appears where the emulsion surface is exposed or activated, and this process therefore It is considered to be a negative type process in contrast to the positive type process of conventional silver diffusion transfer. After the concentrating gradient of silver nuclei has been formed, a one-bath processing step is carried out. The developer-solvent-bath solution performs several functions. It develops and thus enlarges the silver nuclei of the latent image, dissolves the silver halide within its body, forms complexed silver ions, and provides the reducing agent necessary for the solution physical development process, i.e., development The complexed silver ions are reduced and precipitated to the silver precipitation nuclei of the latent image therein. Thus, the main steps to form a reflective silver surface refer to the formation of a surface latent image or the density gradation of silver precipitation nuclei in the data recording area near the surface of the emulsion, and the concentration gradient of silver grains into groups. Using a special monobath solution containing a developer and a complexing agent to grow them until they begin to concentrate, thereby increasing the volume concentration of silver in the surface latent image area until it becomes sufficiently reflective. means.

An alternative method is to coat the entire surface with silver precipitate nuclei that are exposed to light in areas where data directed to the control mark is not recorded, otherwise the layer of silver precipitate nuclei is combined with halogenation. The solution is to use a silver emulsion.
After this, a chemical developer is used to provide a black control mark or other predetermined marking, and finally a monobath developer of the special type mentioned above is used to ensure that it is sufficient in the data recording area. used to grow the silver particles until they become reflective. As a result, reflective laser recording and data storage media consist of reflective silver particles concentrated near the surface of an essentially transparent gelatin matrix. Some of the major processing steps can be achieved by physical phenomena, chemical processing or manufacturing techniques, but when these steps are chained together in a suitable processing order, the result is a reflective laser recording. produce a medium.

Table 1 shows 14 experimental examples, illustrates some of the individual step variations used, and provides a discussion of the two major steps necessary to form a laser recording medium of sufficient reflectivity. Note that the 14 examples in Table 1 include the formation of latent surface images with actinic radiation, aqueous and gaseous fogging agents with hydrazine, and gaseous fogging agents with potassium borohydride.

If a core layer is not added in the preparation of the emulsion,
An important step is the formation of the surface latent image in the data recording areas, and as mentioned above, if the nuclear layer is already provided and is desired to be prerecorded, then the surface latent image is formed in the non-data recording areas. must be formed. Any silver halide emulsion may be used to form the reflective silver surface and is not limited to the use of gelatin-based emulsions. Other film-forming colloids may be used as carriers. Monobath solutions of developer and complexing agent are formulated using a variety of developer and solvent/silver complexing agents. Table 1 lists four types of developers, three types of solvents/complexing agents, five types of emulsions, and four types of surface activation. Reflectance is 15% to 75%
reached the range of Example D In U.S. Patent Application Ser. It is formed by exposing a silver halide emulsion in successive steps to form a partially conductive mirror-like reflective top layer.

Recording is accomplished by melting spots of gelatin in the reflective layer. This storage medium is formed in four steps. Silver halide photosensitive media are exposed to unsaturated actinic radiation to form a latent image that is photographically developed to produce a layer of filamentary silver grains with an absorbing underlying gray optical density. exposed to light. No fusing step is used since the remaining silver halide is used to form the desired reflective layer.

The medium is protected from actinic radiation after the initial exposure by the final bath step. The surface is fogged to form a thin surface layer of silver precipitation nuclei.

Fogging agents such as lithium, sodium, potassium, cesium and rubidium borohydrides are effective.
One thin layer of nucleating agent could be bonded to the emulsion layer due to alternating silver precipitation. After forming a thin layer of silver precipitate layer on the surface of the silver halide photosensitive medium, the final step of the method of the invention involves the transfer of silver in the residual silver halide to the silver precipitate nuclei and the complexation therein. Accompanied by the reduction of silver by silver oxide. This treatment is usually accomplished by placing the nucleated photosensitive medium in a single bath solution. This monobath solution contains both a silver halide solvent and a silver reducing agent. This step is also performed in the dark or with a safelight until the silver diffusion transfer is complete. The two components of this monobath solution, silver halide solvent and silver reducing agent, constitute the silver diffusion transfer and reduction system as described in Example C.

The silver halide solvent acts on the silver halide in the photosensitive medium to produce mobile silver complex ions. These free silver complexes are transported within and across the surface of the photosensitive medium. These silver complexes are susceptible to reduction and form metallic silver in the silver core and in the filamentary silver at the surface.

[Brief explanation of drawings]

Figures 1a and 1b show cross-sectional views of the double-sided silver halide photosensitive material of the present invention. FIG. 2 is a plan view of a substrate pedestal for forming laser recording and data storage media. FIG. 3 is a perspective view of a mounting platform used to apply double-sided silver halide coatings. FIG. 4 is a cross-sectional view of a double-sided silver halide photosensitive material placed on separate substrates bonded together. In the figure, 13, 33, 57 are substrates, 21, 23, 3
1, 35, 53, 55 represent emulsions.

Claims (1)

[Scope of Claims] 1. A photosensitive material consisting of a substrate having two parallel and opposing principal surfaces, each principal surface having a fine-grained photosensitive silver halide emulsion thereon. , a material in which the particle size is typically 0.05 microns. 2. The material of claim 1, wherein the substrate is opaque. 3. The material of claim 1, wherein the substrate is transparent. 4. The material of claim 1, wherein each emulsion contains a light-absorbing dye to attenuate transmitted light into the emulsion. 5. The material of claim 1, wherein each emulsion includes a core layer distributed parallel to the major surface of the substrate and having a maximum concentration distal to the nearest major surface. 6. The material of claim 1, wherein each emulsion has a light-sensitive portion and a light-insensitive portion, said light-insensitive portion comprising a photographically processed indicia pattern. 7. The material of claim 1, wherein the substrate is annular. 8. The material of claim 1, wherein the substrate comprises a plurality of members bonded together. 9. A light-sensitive material consisting of an opaque substrate having two parallel substantially planar opposed major surfaces, each major surface having a light-sensitive silver halide emulsion fixed thereto; material. 10. The material of claim 9, wherein each emulsion includes a core layer distributed parallel to the major surface of the substrate and having a maximum concentration distal to the nearest major surface. 11. The material of claim 9, wherein each emulsion has a light-sensitive portion and a light-insensitive portion, said light-insensitive portion comprising a photographically processed indicia pattern. . 12. The material of claim 9, wherein the substrate is annular.