Raw gold refers to gold that has not been refined or processed into standardized bullion, typically found as unrefined nuggets, flakes, or gold-bearing ore. Verifying the authenticity and determining the purity of these raw forms is a necessary step for anyone who has acquired a new find or is considering a purchase. Because gold is often found mixed with other minerals or alloyed with different metals, a series of testing methods must be employed to accurately assess its true value. These tests range from simple physical checks to more complex chemical measurements that reveal the precise gold content.
Simple, Non-Destructive Preliminary Checks
The first step in evaluating raw gold involves quick, non-destructive physical checks that eliminate obvious fakes and base metals. Pure gold is naturally non-magnetic, making the magnet test a simple screening method. If a strong magnet attracts the sample, it indicates the presence of ferrous metals like iron or nickel, suggesting the item is not pure gold or is heavily alloyed. However, many non-gold metals are also non-magnetic, so a lack of reaction only confirms the absence of magnetic alloys.
A careful visual inspection can also reveal important clues about authenticity. Genuine raw gold maintains a consistent yellow color without signs of tarnish, as the metal is chemically inert and does not oxidize. If the sample displays discoloration or a different color showing through scratches, it is likely gold-plated or a thin alloy. The concept of “heft” is another simple physical check, relying on gold’s high density; real gold feels noticeably heavier than most similarly sized common metals.
The Specific Gravity Method
The specific gravity method, also known as the density test, is the most reliable physical technique for determining gold purity without damaging the sample. Specific gravity is a dimensionless ratio comparing a substance’s density to the density of water, a unique physical property for every element and alloy. Pure, 24-karat gold has a specific gravity of approximately 19.3, meaning it is 19.3 times denser than water.
To perform this test, a high-precision scale and a container of water are required, along with a setup to suspend the gold sample. The first measurement taken is the precise weight of the gold sample in the air. The sample is then fully submerged in water, ensuring it does not touch the container, and its weight while suspended in water is recorded.
The specific gravity is then calculated using a simple formula: the weight of the item in air divided by the difference between the weight in air and the weight submerged in water. A result close to 19.3 suggests high purity, while a significantly lower number indicates the presence of less dense alloying metals. The accuracy of this method relies on meticulous measurements and is especially effective at detecting counterfeits made from materials with lower densities.
Performing the Acid Purity Test
The acid purity test is a definitive chemical method used to accurately determine the karat value of a gold sample. This test uses the principle that gold is a noble metal, meaning it is highly resistant to corrosion and most acids, particularly nitric acid. Because this process involves corrosive chemicals, it must be performed in a well-ventilated area while wearing protective equipment, such as safety goggles and gloves.
The procedure begins by scratching the raw gold sample across a specialized abrasive touchstone, leaving a visible streak of the metal. This deposit is tested with acid reagents sold in kits containing various strengths corresponding to standard karat values like 10K, 14K, and 18K. Nitric acid is typically applied first, as it reacts with and dissolves most base metals alloyed with gold, such as copper and silver.
If the streak disappears or changes color, it means the metal is either not gold or has a purity lower than the acid strength used. If the streak remains unaffected, progressively stronger acids are applied until a reaction is finally observed. The strongest acid that fails to dissolve the streak provides a close estimate of the gold’s true karat rating.
Interpreting Test Results and Purity Scales
The results from both the specific gravity and acid tests are translated into the established Karat system to determine the sample’s purity. The karat system divides the whole into 24 parts, where 24 Karat (24K) represents pure gold (99.9% gold content). Lower karat values indicate the proportion of gold mixed with other metals, or alloys, which are typically added to increase durability.
For example, 18K gold contains 18 parts gold out of 24, resulting in 75% purity, while 14K gold is 58.3% pure. A specific gravity reading of 19.3 confirms a 24K sample, while a result in the range of 15.5 to 17.8 would correlate with 18K to 22K gold, reflecting the presence of common impurities like silver or copper. The acid test provides a direct confirmation of this karat level by identifying the highest-strength acid the gold can resist. If the tests yield ambiguous results, professional analysis is available. Specialized non-destructive methods, such as X-ray fluorescence (XRF) spectrometry, can analyze the elemental composition of the sample with high precision.