Specific gravity (SG) is the ratio of a substance’s density to the density of a reference substance. The reference substance is nearly always distilled water, which has an SG value of 1. Anything with a specific gravity greater than 1 sinks and anything with a density less than 1 floats. Specific gravity is commonly used to find the density or concentration of materials such as chemicals, fuel, beverages, etc.
For jewelers and pawnbrokers, specific gravity testing can be used to assay the carat weight of loose gemstones or the karat rating of gold. The testing method is completely non-destructive – making it perfect for assaying delicate antiques, collectors’ coins, and anything that shouldn’t be marked in any way.
We don’t offer specific gravity testing at MGS, but for good reasons. For starters, the testing method is time consuming compared to other types of assays. On top of that, the test only provides accurate results for individual materials. For example, a plain wedding band or a loose diamond are perfect candidates for specific gravity testing. Conversely, set gemstones or jewelry with adornments that contain different materials (e.g. a gold brooch with aluminum rivets) are not.
Since we are a precious metal refinery that specializes in bulk processing and prides itself on speedy service, you can see why specific gravity testing wouldn’t be a good fit for us. However, it’s an accurate and useful assay for many of our clients. In our infographic below, we’ll show you how to conduct specific gravity testing with minimal equipment.