Assaying is the process of determining the composition of a material. Gold assaying focuses on determining the quantitative content of gold in terms of percentage in a gold product. Assaying of a gold product is key as the price or value of the gold product is highly dependent on the gold content of the said product.
We carry out fire assaying of gold items, which is also known as the cupellation method, as follows:
We carry out gold assaying on all of our scrap gold bars and all of our in-process gold materials such as rods wires, chains, and beads. We also carry out gold assaying on some of the finished gold jewellery products that we sourced from external manufacturers. As fire assaying is a destructive method of ascertaining the gold content, this is only undertaken on a case-by-case basis.
Our gold assaying process begins with taking a sample of the items to be assayed. The said sample will then be further cut into 3 smaller samples. The smaller sample is weighed using a gold balance scale. It is then wrapped in lead foil together with silver and subsequently, copper is added to the samples.
(ii) Heating and annealing
We will prepare cupels which are shallow porous cups by preheating them inside a muffle furnace at 800 °C. Once preheated, the samples are placed in individual cupel and inserted back into the muffle furnace to be heated at 1,100°C. Subsequently, the cupels are taken out and rested at room temperature.
The samples are then cleaned and annealed at 800 °C to reduce the hardness of the material. The samples are then rolled and formed into a strip form.
(iii) Acid wash
The samples will then go through an acid wash using nitric acid to remove any impurities thereby leaving the pure gold content only.
(iv) Final weighing
Subsequently, the samples will go through an annealing process to create a compact form to be weighed to determine its gold purity. The purity result is then recorded and sample will be stored up to 2 weeks.