Credit Card

Abstract

A credit card having a coating of a substance which when treated sufficiently permanently and irreversably changes from a first state having one characteristic of reflectivity for visible light components incident thereon to a second state having a second characteristic of reflectivity for the light components. Preferably, in the first state the substance is highly light reflective, and reflects light of different wavelengths unequally, and in the second state the substance is light transparent. Treating of the substance is accomplished by heating the substance, preferably with a high intensity light beam. Authenticity of the credit card is achieved by first measuring the amplitude of visible light components (colors) reflected by the substance when the substance is treated intitially, and by a later spectral reflectance test after additional treating which, by sensing the change in amplitude of a previously highly reflected visible light component, indicates that the substance has changed to the second state in response to the additional treating. The coating is deposited on a layer of a highly light absorptive material which enhances the reflectance contrast between the first and second states of the coating and promotes rapid treating of the coating.

Description

BACKGROUND OF THE INVENTION

Consumable credit cards have long been used as a means for purchasing services in advance and at a reduced rate. For example, in the commuter transportation industry, multi-ride cards have been used extensively to provide a reduced rate per ride, the cards being physcially manipulated, notched or punched by an attendant each time they are used. similar cards have been used in other multi-use service areas, such as cafeteria services, or vending machine services. These cards are generally made of a soft material which allows them to become bent and defrayed.

A recent development in commuter transportation systems involves the use of automated ticket processing machines for entrance and exit gates at the various stops along the transportation system. A commuting passenger using the system will initially purchase, such as from a vending machine, a multi-ride ticket which on one side has various instructions for the use of the ticket and on the underside has a printed value grid. The ticket also has a magnetic, iron oxide, recording strip on its underside, on which is magnetically recorded, by the vending machine, information such as the value of the ticket and the date.

To gain entrance to the transportation system, the passenger inserts the ticket into the automatic entrance ticket machine at an entrance gate which includes a turnstyle. The pertinent functions of the ticket machine are that it magnetically records the station location on the magnetic recording strip, opens the turnstyle to admit the passenger, and returns his ticket. No marks are made on the value grid. when the passenger disembarks at his station, he places his ticket in the automatic exit ticket machine at an exit gate which also includes a turnstyle. This ticket machine, and cooperating computer apparatus, determines the validity of the card and, from the magnetic recording, if the ticket has sufficient value for the ride just completed, places a mark in the grid to show the degraded value of the ticket, opens the turnstyle, and returns the ticket. If the recording upon the ticket shows insufficient value for the ride when the ticket is placed into the ticket machine at the exit gate, the turnstyle will not open, and the passenger must consult the station agent. The mark in the grid is only for the information of the person owning the ticket; as far as the ticket machines are concerned the value of the ticket is indicated by the magnetic recordings thereon.

Another type of credit card used for commuter transport systems includes dielectric members which are laminated together and externally printed with grid squares which indicate the worth of the ticket. Conductive ink marks or strips underlie the rows of grids from edge to edge of the document. The member carrying the strips is thin, so that a marking tool impressed in a grid will electrically alter the conductivity of the strip. When inserted into an exit control apparatus, the apparatus determines the number of uncut strips to ascertain the value of the card which is rejected when an insufficient value is indicated.

One drawback of the above cards, described in detail in U.S. Pat. No. 3,470,359, is that the cards are easily altered. Thus, it would be fairly easy for a knowledgable person to copy the magnetic recordings of the first-described card onto a used card, after mechanically erasing its old recordings, or to place a similar recording on a ticket-sized card. Similarily, a knowledgable person could alter the conductivity of the conductive strips of the second-described card. In addition, the previously described cards do not provide the card user with a clear indication of the remaining value of a partially-used card, and they are expensive to manufacture.

Another area in which automated apparatus has been used to distinguish between real and counterfeited documents is in currency changing machines and vending machines. In one common type of such apparatus, described in U.S. Pat. No. 3,480,785, the document to be inspected is positioned to receive light, and a plurality of sensors are positioned to receive light reflected from preselected discrete areas on one surface of the document and to provide signals in response to the spectral content thereof. Such signals must be within predetermined amplitude limits for the apparatus to accept the document as authentic. Although these systems may provide satisfactory results for currency cashing, they would not be usable with consumable credit cards, because these systems do not provide an indication of the present value of the card after partial use of the card and do not alter the characteristics of the document tested in any way.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved credit card.

It is a further object of the present invention to provide a credit card that is difficult to counterfeit and manipulate.

It is a further object of the present invention to provide a consumable credit card.

Another object of the present invention is to provide a consumable credit card which can be tested to determine validity and so constructed that the user can easily determine remaining value.

A further object of the present invention is to provide an improved method for testing the validity of a credit card.

In accordance with the invention, the aforementioned objects are attained by a credit card which is provided with a coating of a substance which, when treated sufficiently, is permanently altered or changed from a first state having one characteristic of optical reflectance for light components incident thereof to a second state having a different characteristic of optical reflectance for the light components. Since treating (as by absorbing heat from an incident light beam) can be applied progressively to selected areas of the coating, and the change in the optical reflectance of the treated areas is permanent, not temporary or reversible, and appears as a darkening of those areas of the coating, optical inspection of the credit card, by man or machine, provides an indication of the remaining credit worth of the credit card. A light absorptive strip is provided on one side of the coating to enhance the optical contrast between the areas of the coating that are in the first state and areas of the coating that are in the second state and to promote rapid heating of the coating.

Authentication of any area of the alterable coating of the credit card is achieved by first measuring the amplitude of visible light components (colors) reflected by the area of the alterable coating when that area is in the first state and, thereafter, by measuring any change in amplitude of a previously present visible light component, thereby to indicate that the area has changed to the second state. If the components of the reflected light have the correct amplitude relationship during both measurements, an output signal is generated which permits the credit card to be accepted and a single use to be made of the credit card. With each valid use of the credit card, and where multiple use of the card is desired, the credit card is indexed to a new position, either manually by the user or automatically, such that an adjacent area is tested. If the result of either measurement is incorrect for all areas of the credit card, the credit card is not accepted. A patent application having claims directed to testing of the credit card, entitled "Apparatus for Testing a Credit Card" Ser. No. 361,742, filed May 18, 1973, now U.S. Pat. No. 3,795,805 and assigned to the same assignee as the present invention, was filed concurrently with this application.

Other objects of the invention will become readily apparent to those skilled in the art in view of the following detailed disclosure and description thereof, especialy when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of the credit card of the present invention.

FIG. 2 is a perspective view of the authentification apparatus used with the credit card of FIG. 1.

FIG. 3 is a schematic view of the optical system of the apparatus of FIG. 2.

FIG. 4 is a schematic diagram of one portion of the electrical components of the apparatus of FIG. 2.

FIG. 5 is a schematic diagram of the logic circuit of the apparatus of FIG. 2.

FIG. 6 illustrates waveforms produced during testing of the alterable substance forming part of the credit card of FIG. 1.

FIG. 7 is a schematic diagram of a motor stepping circuit than can form a part of the apparatus of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is applicable to all areas where credit cards are used to control unattended apparatus. Specific areas in which the invention is useful is in the field of commuter ransportation and transportation machines. The invention is particularly useful in the field of copy and duplicating apparatus. In the latter application, the customer would purchase the credit card from a librarian, book store, supermart, etc. at a reduced rate per copy, insert the credit card into a copying machine, dial the number of copies desired (up to the maximum allowed by the card), and press the print button. If the credit card is authentic and has value to cover the number of copies dialed, the customer receives his desired number of copies and his card is returned with a dark area on it for each copy made. The dark areas allow the customer to tell at a glance how many copies' worth remain on the card and prevents the unattended apparatus from producing another copy chargeable to a previously used area. When the card has been exhausted, a new card is purchased. Some advantages of this type of credit card purchase are reduced rate per copy credit card convenience, and eliminated coin box pilferage.

Referring now to FIG. 1 of the drawings, the credit card 2 typically comprises two layers 4 and 6 of clear vinyl plastic or other stiff transparent material. Layers 4 and 6, typically 0.025 inch and 0.005 inch thick, respectively, are laminated together, such as by a transparent, pressure sensitive adhesive. A strip of light absorptive (black) paper 8, preferably about 0.005 inch thick, is positioned between layers 4 and 6. A thin, preferably 0.001 inch to 0.005 inch thick, coating 10 of a heat-alterable substance is applied to one surface of paper 8. Coating 10 can be applied by masking all but the paper 8 and spraying the heat-alterable substance onto the exposed surface of paper 8. Obviously, the application of coating 10 is achieved prior to laminating together layers 4 and 6.

The substance used as coating 10 is selected from a group which have different optical reflectance characteristics at different temperatures, that is, substances that have a given spectral reflectance characteristic under one condition, that is, within a first range of temperatures, and a different spectral reflectance characteristic under a second condition, that is, within a second range of temperatures higher than the first range of temperatures. The transition temperature from the first range to the second range is referred to as the critical temperature, or "burn" temperature. A preferred group of substances of this type is sold by Tempil Corporation of South Plainfield, N.J., under the trademark "Tempilaq." These substances reflect light frequency components (colors) having desired amplitudes when within the first range of temperature and, when heated to within the second range of temperatures, do not reflect in large amplitude at least one of the previously reflected light frequency components. Specifically one such substance, that is, "Tempilaq" No. 175F, reflects a large amount of blue light, a smaller amount of green light, and a still smaller amount of red light (the reflected light appearing blue to the human eye) when heated to less than 175.degree.F but very little blue light when heated beyond the "burn" temperature of 175.degree.F. "Burn" or change of state takes less than 5 milliseconds. Another acceptable group of materials for coating layer 10 is sold by the William Wahl Corporation of Santa Monica, Calif., under the trademark "Temp-Plate."

Since in one of its intended purposes, the credit card will provide for multiple credit changes, adjacent areas of the coating 10 can be heated for each credit charge. Heating of the separate areas is achieved preferably by indexing the credit card horizontally or vertically, either manually or by automated apparatus If desired, boarder strips can be provided between adjacent areas of the coating 10 to isolate them such that only one area at a time is heated, such as by a high intensity light beam.

Due to the change in state and associated change in spectral reflectance (amplitude of colors reflected) of coating 10 when heated beyond the critical temperature, two separate tests can be performed to check the validity of the credit card. The first test analyzes or measures the amplitude of light components (colors) reflected from coating 10 when it is in its first state, that is, when it is below 175.degree.F in the case of "Tempilaq" No. 175F. This test data is processed (integrated) to sharply define the amplitudes of the reflected colors and then the waveforms indicative of the color amplitudes are supplied to logic circuitry which provides a first test signal indicative of the proper color amplitudes. The second test provides an indication that the coating 10 has changed state or "burned" due to continued heating, that is, that the amplitude of one of the reflected colors, blue in the case of "Tempilaq" No. 175F, has decreased greatly. This decrease in amplitude and the first test signal are utilized by the logic circuitry to provide a signal indicative of an authentic credit card. The change of state of a heated area of coating 10 also provides a permanent and irreversible indication, to the user and to the associated authentification apparatus, that the area of the coating has been used for a credit purchase. In the case of "Tempilaq" No. 175.degree.F, a solid (or possibly super cooled liquid) is formed after cooling from above 175.degree.F.

The substance of coating 10 is different from liquid crystals used to produce temporary displays, as described in U.S. Pat. Nos. 3,637,291 and 3,524,726. Although the substances described in the above patents evidence two chromatic states, i.e., a first translucent state and a second opaque state, when heated to a predetermined temperature, the substance must be able to reverse states to provide the desired change in visable display. This reversal is accomplished by the removal of the heat. It is therefore necessary to continuously apply energy to the liquid crystal material in order to display the images for extended periods of time, since the change in light-reflecting properties is not stable.

The manner in which the credit card 2 can be used is best explained by reference to FIGS. 2 and 3 which show apparatus for testing the validity of credit card 2. A lamp 14, with the aid of a collecting mirror 16, projects a high intensity light beam through lens assembly 17 toward a credit card holder 18 which has channels (not shown) for holding the credit card. Lamp 14 can be a 12 -volt 150-watt tungsten halogen lamp. An apertured shutter 20 is positioned between the lamp 14 and the holder 18 to intercept the light beam at all times except when the validity tests are to be performed. To restrict the area of the light beam impinging upon card 2 when it is between the support channels, an apertured mark 19 is positioned adjacent the holder 18 on the side thereof facing lamp 14.

In operation, when the credit card 2 is inserted between the channels of holder 18, a switch is tripped which permits energization of a solenoid 22 which moves shutter 20 to the right, thereby allowing light to be projected through the aperture in shutter 20 and onto a selected area of coating 10. Timing means (not shown) are provided such that shutter 20 is in the light transmissive position for the duration of testing, about eight tenths of a second when "Tempilaq" No. 175F is used as the subtance of coating 10. If desired, a shoulder, keyway, or other suitable indexing means may be included in the structure of credit card 2 to require a specific orientation of the card before it may be entered into the holder channels, thus obviating the user visually orienting the card for face-up operation.

As previously mentioned, when coating 10 is "Tempilaq" No. 175F, initial heating (heating below 175.degree.F) produces a spectral reflectance spectrum having a large amplitude blue component, a smaller amplitude green component, and a still smaller amplitude red component. When strip 10 is heated sufficiently, about 175.degree.F, which occurs after about 0.7 seconds of exposure to a high intensity light beam, such as produced by a 150 -watt tungsten halogen lamp, the coating 10 "burns," changes state, with the result that coating 10 becomes transparent thereby exposing the highly light absorptive strip 8 to the photoconductors 28, 29 and 30 whereby the amplitudes of the blue, green and red components of the reflected light decrease rapidly. These color-temperature characteristics of coating 10 are used to produce two test signals, as will now be explained.

Positioned adjacent to the support 18 is a photoconductor assembly which includes three light filter-photoconductor combinations. Specifically, photoconductors 28, 29 and 30 cooperate with filters 32, 33, and 34, respectively, which (when coating 10 is "Tempilaq" No. 175F) transmit blue, green, and red light, respectively. Accordingly, only the blue component of the light reflected by coating 10 of credit card 2 is incident on photoconductor 28; only the green component of the reflected light is incident on photoconductor 29; and only the red component of reflected light is incident on photoconductor 30. A funnel-shaped shield 36 is positioned adjacent the filters 32, 33 and 34 and the credit card support 18 to prevent stray light (light not reflected by a heated area of coating 10) from contributing to the conductivity of the photoconductors 28, 29, and 30. If desired, light conducting fibers may be used to conduct the reflected light to the location of the filter-photoconductor conbination as a further preventative against erroneous signals produced by stray light.

Photoconductors 28, 29 and 30 form parts of conventional integration circuits 40, 41, and 42, respectively, as shown in FIG. 4. With the coating 10 of "Tempilaq" No. 175F having the spectral reflectance sequence previously set forth, that is, reflectance of a large amount of blue light, a smaller amount of green light, and a still smaller amount of red light prior to "burn," with a decrease in the amplitude of these colors reflected by coating 10 after it "burns" or changes state, the output waveforms of the integrators 40, 41 and 42 will be as shown in FIG. 6. As indicated by FIG. 6, the output waveform of integrator 40 (blue light) reaches a high value or amplitude (due to the large amplitude of blue light reflected) prior to the time that the output waveforms of integrators 41 (green light) and 42 (red light) reach a high level, with the output waveform of integrator 41 (green light) reaching a high value before the output waveform of integrator 42 (red light) reaches a high value (due to the large amplitude of green light reflected than red light reflected). FIG. 6 also shows that the output waveform of integrator 40 decreases rapidly once the strip 10 "burns" or changes state.

The output signals of integrators 40, 41 and 42 are supplied to input terminals of a logic circuit (FIG. 5) which is one form of logic circuit that can be used to make the determination of whether the amplitudes of the light components (colors) reflected by coating 10 is proper when coating 10 is in the first state (first test), and whether the amplitude of the blue component of the reflected light diminishes rapidly when coating 10 is heated sufficiently to change state (second test). Referring specifically to FIG. 5, the output of integrator 40 (blue light waveform) is supplied to the D input terminal of a flip-flop 50 and to one input terminal of a NOR gate 52. The output of integrator 41 (green light waveform) is supplied to the CL (clock) input of flip-flop 50. The Q or high voltage output of flip-flop 50 is coupled to the D input of a flip-flop 54. The output signal of integrator 42 (red light waveform) is supplied to another input of NOR gate 52. The third input to NOR gate 52 is connected to a dropping resistor 56 which has its non-ground side connected to a dc source through a switch 57 which is open only when shutter 20 is permitting light from lamp 14 to illuminate coating 10 or an area thereof. The output terminal of NOR gate 52 is connected to an input terminal of a NOR gate 58 which forms part of a clamping circuit 60. Circuit 60 also includes a NOR gate 62 which has its output signal feedback to a second input terminal of NOR gate 58. The output terminal of gate 58 is connected to an input terminal of gate 62, the other input terminal of gate 62 being connected both to the non-grounded side of a dropping resistor 64 and to a dc source via a switch 66.

In operation of the circuit of FIG. 5, the output of NOR gate 50 will be positive only if all the input signals thereto are negative. This will occur only when the spectral pulses occur in the sequence shown in FIG. 6 and the coating 10 "burns." In the proper sequence, the leading edge of the green signal will provide a clock pulse while the blue signal is positive, producing signal at the output of flip-flop 50, thus arming flip-flop 54. The leading edge of the red signal clocks flip-flop 54 after it is armed, producing a negative signal at the lower input terminal of gate 52. Shortly thereafter, the blue signal decreases, producing a negative going signal at the middle input of gate 52. Since the signal applied to the top input terminal of gate 52 is always negative (ground) when the shutter 20 is open (about 0.8 seconds), the proper sequence of colors produces negative pulses at all three input terminals of NOR gate 52 and thus a positive signal at the output terminal of NOR gate 52. The latch circuit 60 provides a permanent indication of the positive signal at the output of gate 52. The output of gate 62 of the latch circuit 60 is coupled to control circuitry (not shown) which reacts only to a positive signal to induce operation of a machine, such as a copier. When the machine has cycled, the switch 66 is closed, providing a high voltage signal to the lower input of gate 62, with the result that the output of gate 62 becomes negative. NOR gate 52 is reset by the closing of switch 57 when the shutter 20 closes.

If the coating 10 did not "burn" or change state, that is, did not cease to reflect a large amount of blue light, the input signal to the middle input terminal of gate 52 would remain positive and the output signal thereof would not become positive. If the amplitude of the reflected colors, and accordingly, the timing sequences of pulses produced by the integrator networks 40, 41, and 42, did not occur as desired, for example, if the ampitude of the red signal was too large and the edge of the high voltage signal produced by integrator 42 occurred before either the integrated blue or green signals attaining a high value, the flip-flop 54 would be clocked prior to being armed, and a negative going signal would not appear at the bottom input terminal of gate 52. Similarily, if the leading edge of the integrated green signal did not attain a high value while the integrated blue signal was at a high value, the flip-flop 54 would not be armed, and it would not produce a negative pulse upon the occurrence of a clock pulse. Accordingly, the logic circuit of FIG. 5 indicates that the color amplitudes are correct, and that the coating 10 has "burned."

As previously mentioned, when the credit card is to be used for multiple credit purchases, the coating 10 will be divided into discrete areas, each area representing a single credit purchase. In the case of multiple purchases, the testing equipment would include apparatus (indicted generally as 70 in FIG. 2) for transporting the credit card horizontally and vertically such that the light from lamp 14 can be made to fall sequentially on adjacent areas of the coating 10 of credit card 2. When the credit card is used with a copying or duplicating apparatus, the credit card would be indexed such that the desired number of copies can be made.

Obviously, the testing apparatus would include apparatus (not shown) which would index the transport system to the first unburned area of the credit card. This could be achieved by a photoconductor positioned adjacent the coating 10. If a light beam, either produced by lamp 14 or by another light source, incident on an area of coating 10 does not provide a minimal of reflected light (incident on the photoconductor) within a few tenths of a second, indexing apparatus would move the credit card holder to a new position such that light now falls on an adjacent area of coating 10. A typical stepping motor control circuit which could be used to move or index the credit card when it is intended for multiple purchases is shown in FIG. 7. Each time that switch 57 closes the relay switch R is closed, momentarily resulting in the conduction of controlled rectifier Q.sub.1 `and, as a result, the conduction of controlled rectifier Q.sub.3. The current flow through the motor control winding, as a result of conduction of controlled rectifier Q.sub.3, is sufficient to produce one increment of revolution of a motor shaft which is coupled to holder 18, such as through an appropriate gear train. Accordingly, the holder 18 would move one increment, depending upon the size of the discrete areas of the coating 10, each time that the shutter switch 57 is closed.

In addition to defining the second spectral reflectance after coating 10 has changed to a transparent liquid (and then to a solid on cooling), highly light absorptive strip 8 serves two other functions. First, it absorbs radiant energy incident thereon thereby reducing the time necessary to heat coating 10 to the "burn" temperature. Second, it absorbs the liquid of coating 10 when it changes to a liquid state thereby helping to prevent the possibility of mechanically manipulating the substance of coating 10 once it has changed state.

While the present invention has been described with reference to preferred arrangements, it will be understood to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. Specifically, a different color light absorptive strip 8 could be used instead of black. If strip 8 were red, the second authenticity test would indicate that the amplitude of blue light reflected by the card had decreased substantially, while the magnitude of red light reflected had increased substantially. In addition, the bandwidth of the light filter can be changed to correspond to the light colors used to test the validity of the credit card, and the coating 10 or any area thereof can be heated by apparatus other than lamp 14. Additional filters could be included between the lamp 14 and the credit card holder which would permit the passage of infrared light and light of those colors used in testing the credit card.

Claims

What is claimed is:

1. A credit card comprising

a support layer, and

a coating of heat-sensitive substance supported by said layer, said heat-sensitive subtance being responsive to energy from a remote source incident upon said substance and having a first optical reflectance characteristic when within a first temperature range, and a second, different optical reflectance characteristic when heated to a temperature beyond said first temperature range, said second optical reflectance characteristic of said substance being permanent even when exposed to said energy from said remote source once said substance is heated beyond said first temperature range.

2. The credit card of claim 1 in which said heat-sensitive substance comprises a material which is light reflective when within said first temperature range, and which is light transparent when heated to a temperature beyond said first temperature range.

3. The credit card of claim 1 wherein said heat-sensitive substance comprises a material which is highly reflective of light of a given frequency when within said first temperature range, and which is not highly reflective of light of said given frequency when heated beyond said first temperature range.

4. The credit card of claim 3 wherein a sheet of a highly light absorptive material is positioned between said support layer and said coating of said heat-senstive substance on said support.

5. The credit card of claim 4 said light of said given frequency is blue and said sheet of highly light absorptive material is black.

6. The credit card of claim 2 wherein said material reflects a large amount of blue light, a lesser amount of red light, and a still lesser amount of green light when within said first temperature range.

7. A credit card comprising

a support layer,

a coating of a heat-sensitive substance supported by said layer, said heat-sensitive substance being reponsive to energy from an external source incident upon said substance and having a first range of light reflectance when within a first temperature range, and a second, different range of light reflectance when heated to a temperature beyond said first temperature range, the second range of light reflectance of said substance being permanent even when exposed to energy from said external source once said substance is heated beyond said first temperature range, and

means positioned between said support layer and said coating of a heat-sensitive substance for enhancing the optical contrast between said first and second optical reflectance characteristics of said heat-sensitive substance.

8. The credit card of claim 7 in which said heat-sensitive substance comprises a material which is highly reflective when within said first temperature range, and which is highly light transparent when heated to a temperature beyond said first temperature range.

9. The credit card of claim 7 in which said heat-sensitive substance comprises material which is highly reflective of light of a given frequency when within said first range, and which is highly transparent to said light of said given frequency when heated to a temperture beyond said second range.

10. A credit card comprising

a transparent support layer

a sheet of a highly light absorptive substance deposited on said support layer, and

a coating of a heat-alterable material on said highly absorptive material, said heat-alterable material being highly reflective of light of at least one color when within a first range of temperatures and transparent to said light of said one color when heated to a temperature beyond said first range of temperatures.

11. A method of testing the authenticity of a credit card having a coating of a heat-sensitive substance having a first optical reflectance characteristic when within a first temperature range and a second optical reflectance characteristic when heated to a temperature beyond said first temperature range, comprising the steps of:

measuring the magnitude of light of at least one color reflected by said substance when said substance is within said first temperature range to produce a first signal representative of the amplitude of said one color,

heating said substance to a temperature beyond said first temperature range,

measuring the magnitude of said light of said one color reflected by said substance when said substance is heated beyond first temperature range to produce a second signal representative of the amplitude of said one color, and

using both said signals to determine the authenticity of said credit card.

12. The method of claim 11 wherein heating of said substance is achieved by a high intensity light beam, said beam also being used in making both said measurements.

13. The method of claim 11 wherein said signals representative of the amplitude of said light of said one color are electricaly integrated.

14. A method of testing the authenticity of a credit card having a coating of a heat-sensitive substance which is light reflective when within a first range of temperatures and light transparent when heated to a temperature beyond said first temperature range, comprising the steps of

producing signals representative of the amplitudes of light of at least two different colors reflected by said substance when said substance is within said first temperature range, and when said substance is heated to a temperature beyond said first temperature range,

electrically integrating each of said signals to derive signals that have a time-amplitude characteristic determined by the amplitude of each of said signals, and

supplying said signals having said time-amplitude relationship characteristic to a logic circuit when said substance is both within said first temperature range and heated to a temperature beyond said first temperature range.