Security device

1. A security device, comprising:

a substrate formed with a surface relief defining an optically variable effect generating structure; and

at least two different opaque reflection enhancing materials, at least one of which is discontinuous, on the same side of the substrate with respect to the surface relief, each of the at least two reflection enhancing materials having the surface relief profile and having different hues, whereby the optically variable effect can be viewed against a background defined by the at least two reflection enhancing materials.

2. A device according to claim 1 , wherein the surface relief defines at least one of a holographic image and a diffraction grating generating microstructure.

3. A device according to claim 1 , wherein the at least two opaque reflection enhancing materials contact said surface relief.

4. A device according to claim 1 , wherein the at least two opaque reflection enhancing materials are provided in respective, different layers on the substrate.

5. A device according to claim 4 , wherein at least one transparent layer having the surface relief profile is provided between the opaque reflection enhancing materials.

6. A device according to claim 5 , wherein the at least one transparent layer between the opaque reflection enhancing materials is a metal oxide having dielectric properties.

7. A device according to claim 1 , wherein the at least two opaque reflection enhancing materials are discontinuous.

8. A device according to claim 1 , further comprising an ink layer between the surface relief and at least one of the at least two opaque reflection enhancing materials.

9. A device according to claim 1 , wherein at least one of the at least two opaque reflection enhancing materials is provided at least in part in a predetermined pattern.

10. A device according to claim 9 , wherein the predetermined pattern is defined by dots or lines having a regular periodicity.

11. A device according to claim 10 , wherein at least one of the at least two opaque reflection enhancing materials is provided in a form so as to define a covert image, which is viewable with a microlens array, lenticular array, or other appropriate optical decoder matched to the periodicity.

12. A device according to claim 9 , wherein at least one of the at least two opaque reflection enhancing materials is provided such that its optical density varies in one or more lateral dimensions.

13. A device according to claim 1 , wherein no opaque reflection enhancing material is provided on a border region of the substrate.

14. A device according to claim 1 , wherein at least one of the at least two opaque reflection enhancing materials is a metal.

15. A device according to claim 14 , wherein the metal is one of aluminum and copper or copper rich alloy.

16. A device according to claim 15 , wherein the metal has been demetallised using an acidic solution based on hydrochloric, sulphuric or nitric acid.

17. A device according to claim 14 , wherein the metal is provided in a pattern which defines a rf resonant circuit.

18. A device according to claim 14 , wherein each of the at least two opaque reflection enhancing materials are metals separated by an insulating layer to define a capacitance.

19. A device according to claim 1 , further comprising a printed image on the surface relief.

20. A document or article of value carrying a security device according to claim 1 .

21. A device according to claim 1 , wherein each of the at least two opaque reflection enhancing materials comprise metals or alloys.

22. A device according to claim 21 , wherein the at least two opaque reflection enhancing materials are discontinuous.

23. A device according to claim 21 , wherein the at least two opaque reflection enhancing materials have been vacuum deposited.

24. A device according to claim 9 , wherein the predetermined pattern is at one of a bar code and indicia.