are characteristic of the sample composition.
6 Using XRF, the average metallic
composition of the Persian daric was
found to be 95.1 percent gold, 2.8 percent
copper and 2.1 percent silver.
Alloy-replicated mirrors
Replicated mirrors were produced using
Darius’ alloy. The intent was to compara-
Figure 3.
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tively characterize the surface hardness
and wear resistance of this unique alloy
against virgin gold and to spectrophotometrically measure its infrared reflectivity.
If improved hardness was evident, then
the alloy might be an ideal candidate for
further surface hardening using a room-temperature deposited protective film.
For comparative hardness measure-
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for Optical & Laser Technologies
ments, the moderate abrasion methods per
MIL-M-13508C were used by abrading
dry cheesecloth across a mirror’s surfaces
using a 1-lb force. Virgin gold suffered visual damage after one test stroke; Darius’
alloy survived eight to 12 strokes.
Reflectivity was measured on PerkinElmer Lambda 950 UV/VIS and Lambda
983 infrared spectrophotometers. In the
1300- to 15,000-nm region, alloy mirrors
were basically indistinguishable from virgin gold (> 99 percent reflectivity).
These alloy-replicated mirrors therefore
were excellent candidates for further surface modifications.
Reactive ion plating deposition
Established as a means to produce high-quality optical filters, Newport’s Stabilife
Reactive Low Voltage Ion Plating
(RLVIP) process was used to deposit hard
adherent silicon protective films upon the
alloy mirror’s surfaces.
7 The process produces optical thin films possessing the
physical density, amorphous microstructure and optical properties approaching
those of bulk materials. These homogeneous films are free of the physical pores
and columnar structure typically seen in
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