Chow Y.S*, Lim T.B, Michael Tay Ming Kiong
International Association of Forensic Sciences, 16th Triennial Meeting
August 2002, Montpellier, France.(poster presentation)
Objectives: This paper presents a survey of the physical properties and chemical composition of commercially available coloured golds which are rapidly gaining popularity.
Nature of the study: Over the years, we investigated several cases of fraud involving precious metals and gemstones. There is a need to further develop our capabilities to identify, characterise and analyse precious metals and gemstones effectively. In this project, the precious metal of interest is coloured gold as this type of gold is fast becoming popular. Physical properties such as colour, density, micro-hardness and microstructure can be used to characterise the different coloured golds. The compositions (including both minor and trace alloying elements) of the coloured golds will also be determined.
Materials and methods: Coloured golds studied in this survey include red, green, blue and purple golds. Microspectrophotometry was used to determine the colour of the different coloured golds. Densities were determined using the Archimedes Principle. Samples of different coloured golds were treated to reveal their microstructure and phases. Composition was then determined using the scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDX). The overall composition of major, minor and trace elements was determined using inductive coupled plasma with mass spectrometry (ICP/MS).
Statistics analysis : Variation in properties will be compared.
Results: In our past cases, we have successfully identified fake precious metals and gemstones. Very often, a non-precious metal is used as the framework of the jewellery which is coated with an outer layer of gold or gold alloy. In another fraud case, we were able to characterise some fake diamonds and successfully identified them as synthetic cubic zirconia. In addition, we will present our preliminary results on coloured golds and techniques that will allow them to be identified and characterised.
Conclusion : By using our casework experience as a foundation for expanding into the field of coloured golds, we hope to correlate the chemical composition of the microstructure of coloured golds to their physical properties and develop a database for the identification of unknown precious metals.