Gold purity refers to the proportion of pure gold in an alloy. Pure gold, 24-karat, is 99.9% gold. Understanding purity is important for assessing value, confirming authenticity, and determining suitability for jewelry or industrial uses. The karat system is the primary measure; higher karat numbers denote greater pure gold percentage.
Simple Purity Checks You Can Do
Simple, non-destructive methods offer preliminary gold purity indications through visual inspection of color. Pure gold is a distinct, rich yellow; variations or dullness suggest lower purity or plating. Wear signs, like discoloration along edges, reveal a base metal beneath plating.
A magnet test quickly identifies non-gold items; gold is not magnetic. If a strong magnet attracts the item, it is not solid gold, though non-magnetic base metals may be present. The density test, less precise for exact purity, indicates if an item is lighter than solid gold of the same size, suggesting it might be hollow or a different material. These basic checks rule out fakes but do not provide definitive purity percentages.
Chemical and Electronic Testing Approaches
Common methods for evaluating gold purity include acid and electronic testers, offering a better indication than visual checks. The acid test, or scratch test, involves rubbing gold onto a testing stone to leave a streak. Different strengths of nitric acid are applied; pure gold will not react, while lower karat gold dissolves or changes color based on purity and acid strength. Safety precautions are necessary when handling corrosive acids, including gloves and eye protection in a well-ventilated area.
Electronic gold testers measure electrical conductivity or resistance. These devices involve placing a drop of testing solution on gold and touching it with a probe. The tester analyzes the electrical response to provide a digital readout of karat value within seconds. While convenient, electronic testers’ accuracy can vary, and they may be less precise for low purities or heavily plated items.
Advanced Laboratory Analysis
Specialized laboratory analyses provide accurate gold purity determination. X-ray fluorescence (XRF) spectrometry is a non-destructive method providing precise elemental analysis. An XRF analyzer directs X-rays at the sample, causing atoms to emit secondary X-rays, revealing the metal’s exact composition, including gold percentage and other alloys. This technique is widely used professionally for its speed and precision.
Specific gravity testing, or density testing, offers another accurate method for solid gold. This involves measuring the item’s weight in air and then submerged in water. Comparing these weights allows calculation of the item’s density, which is then compared to the known density of pure gold and its alloys to determine purity. This method requires careful measurement and specialized equipment but provides reliable purity assessment for non-hollow items.
Understanding Gold Hallmarks and Purity Standards
Gold hallmarks are official stamps on gold items, indicating purity and often the manufacturer or assay office. These marks declare gold content. Common karat notations include “24K” (99.9% gold), “18K” (75% gold), “14K” (58.3% gold), and “10K” (41.7% gold). These percentages reflect pure gold proportion in the alloy, with the remainder being other metals.
European numeric standards also denote purity. For example, “999” signifies 99.9% pure gold (24K), “750” indicates 75% pure gold (18K), and “585” represents 58.5% pure gold (14K). While hallmarks provide an initial indication of purity and authenticity, they are not always a definitive guarantee. Counterfeit items may bear false hallmarks, necessitating further testing to confirm stated purity.