Investigation of turquoise imitations and treatment with analytical pyrolysis and infrared spectroscopy

- Turquoise treatments and imitations have been analyzed by analytical pyrolysis and infrared spectroscopy.
- The capability of analytical pyrolysis in the characterization of polymer coatings was shown.
- Synthetic resins used as binders in reconstructed turquoise identified with pyrolysis-GC-MS.

Turquoise is an opaque mineral with a typical blue green color used in modern and traditional jewelry. As always when there is a higher demand for a material than supply, there is a vital interest for optimizing the product yield (reuse of waste), improving lower quality material or even producing imitations. Very often organic polymers are used in this context and their identification is a challenge not easily accomplished with traditional gemological techniques. The application of infrared spectroscopy and analytical pyrolysis can reveal the true composition of various “turquoise” samples. Whereas the first technique is especially capable of differentiating between natural and synthetic minerals and identifying surface treatments such as wax or polyurethane coatings, pyrolysis is exceptionally well suited to trace not only the surface coatings such as wax, polyurethane or (meth)acrylates, but also to identify binders used in pressing mineral powder (e.g. melamine formaldehyde resins) or epoxy resins which are also used to impregnate porous, otherwise instable materials.