As a platinum buyer this is important to remember platinum metal is expensive relative to most other metals therefore there is always an economic incentive to pass lower content platinum as higher content platinum. Hence, remember to test for platinum purity.
Heating and Discoloration
Platinum should not melt when heated under temperatures below its very high melting point (1768°C). Platinum will also not discolor. This test can be undertaken under a Bunsen flame.
Measure the mass of the jewelry (in grams) and then put the jewelry in a small beaker that has water in and see how much the water level rises (mL). The unit millilitres (mL) is equal to the unit cubic centimetre (cm3) (1 mL = 1 cm3). By dividing the mass in grams by the water displaced in millilitres (mL) you will get the density of the jewelry in grams per cubic centimetre (g/cm3). Pure platinum is 21.45 g/cm3.
Please note that if the jewelry is not platinum this test would be completely destructive. This test involves the use of strong acids so before you begin this test, please ensure you have the personal protective equipment (PPE).
- Safety goggles - to protect your eyes
- Protective gloves - to protect your hands
- Water, baking soda, paper towels - to dilute, neutralize, and clean acid spills respectively.
Also ensure you are in a well-ventilated area as the acids are strong and noxious.
Platinum is resistant to most common acids. However, cold aqua regia (3 part HCl + 1 part H2NO3) will dissolve most metals almost instantly but only dissolve platinum slowly.
This method of testing is non-destructive and is suitable for normal assaying requirements. A computer, called a x-ray fluorescent (XRF) analyzer, will use x-rays to determine the composition the the jewelry. It takes less than a few minutes to complete and the results may be printed out. Popular brands include Thermo Scientific Niton range or Olympus GoldXpert or DELTA Precious Metals XRF analyzers.
There is also a method called x-ray fluorescence assay which involves melting a sample into a uniform composition before testing the sample on a XRF analyzer. This method is more accurate then a XRF analyzer but less accurate then a fire assay.
This method of testing is totally destructive however provides the greatest accuracy. The first part of the process is called fusion which involves mixing the sample with a fluxing agent (which helps melt, fuse, and separate the precious metal) and heating it to a high temperature. The second part of the process is called cupellation which involves using a collector, such a nickel or lead, to extract the precious metals.
The precious metals extracted from fire assay is then analyzed by one of the following methods:
- Flame Atomic Absorption (AA)
- Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES)
- Inductively Coupled Plasma-Mass Spectrometry (ICP-AES)
- Instrumental Neutron Activation Analysis (INAA)
Other equipment that is common in platinum testing kits include:
- Jewelers loupe provides magnification to see small details more closely. Handy for inspecting hallmarks.
- Digital scale for precisely measuring the weight of jewelry.
- Magnet for testing if there are magnetic metals in the jewelry.
- Diamond tester for confirming a precious stone is a genuine diamond (or moissanite).