There are a few methods you can use to test scrap gold to determine its purity and value:

1. Acid test: This involves using a special acid solution to determine the gold’s karat. The acid will react differently to different levels of gold purity, allowing you to determine the karat of the gold.

2. Electronic gold tester: This is a device that uses electrical conductivity to determine the gold’s karat. It’s a quick and easy method, but it can be expensive to purchase a tester.

3. Fire assay: This is a traditional method of testing gold that involves melting down the gold and separating it into its various components. It is the most accurate method, but it is also the most time-consuming and costly.

4. X-ray fluorescence (XRF) spectrometry: This is a non-destructive method that uses an X-ray beam to determine the gold’s composition. It is a quick and accurate method, but it can be expensive to use a spectrometer.

Note that these methods are not foolproof, and the results may not be 100% accurate. However, for our purposes – buying scrap gold and scrap gold jewelry from the Masses – the acid test is sufficient 98% of the time. If you want a more accurate assessment of your scrap gold, say, for example, a seriously valuable piece, you should consider taking it to a professional gold dealer or a laboratory for testing.