2nd August 2013
As a minimum quality control procedure, all gold alloys fabricated for casting and chain making operations are assayed for gold content. This ensures that such products reach minimum assay requirement for each specific caratage. As a general guideline, specifications defined by the ISO 9202:1991 JEWELLERY – Fineness of Precious Metal Alloys Standard, are complied with.
|9 Carat||375 parts per thousand or 37.5% Au|
|10 Carat||417 parts per thousand or 41.7 % Au|
|14 Carat||585 parts per thousand or 58.5% Au|
|18 Carat||750 parts per thousand or 75.0% Au|
|22 Carat||916 parts per thousand or 91.67% Au|
Proprietary company recipe, for various alloys fabricated, provide assurance that negative tolerance against the above specification are not allowed.
We believe a number of our internal specifications for gold (and sterling Ag) alloys are tighter than some industry requirements.
General – A fire assaying technique (comparable to international standard procedures) is in use for gold analysis. The job is handled by a competent assayer/chemist.
For white gold alloys, Atomic Absorption Spectroscopy is used for Platinum and Palladium analysis.
Repeatability/Reproductibility of assay results
Duplicate determination on granulated alloys shall give results differing by less than 0.05% by mass for yellow and red gold alloys and less than 0.10% by mass for white gold alloys. The assay shall be repeated if the difference is greater than the tolerance quoted.
Handling, Sampling and Analysis of materials other than fabricated alloys
- As far as practicable, a composite sample is extracted and is analysed on finished product, e.g. chain products unless a specific sampling procedure has been agreed upon with a customer.
- Findings purchased from suppliers are all randomly sampled and analysed. Lots found to be under carat are returned to suppliers.
- Roasting and dressing of sweeps and roasting and melting of lemel and their subsequent sampling are done by trained refinery personnel.
Analysis of samples follows standard fire assaying procedures.
Pancho A Macalincag
Manager, Analytical Services Department