Holograms that are predominantly in use today as visually identifiable security devices can generally be divided into two categories: either surface relief rainbow holograms or reflection type volume holograms. The Aztec structure is a special surface relief device that combines aspects of both of these types. It has unique identifying characteristics, with provision for great difficulty in counterfeiting, which make it more secure. Its fabrication by holographic means requires techniques of both surface and volume holograms, thus is technically more difficult to make than either separately. The structure is deeper than the standard surface relief hologram, and its profile has the characteristic of several well defined steps, such that, when viewed on edge, resemble a stepped pyramid. Thus, replication of the Aztec structure requires special high resolution techniques to faithfully record the submicron features of the stepped profile, and thus is more difficult to manufacture. The visual characteristics of the Aztec structure are similar to the volume hologram, in that single colors, rather than rainbow colors, can be viewed. Also, a combination of single colors can be encoded into a single master, yielding unique visual effects.
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