6 Ways to Identify a Metal
Whether you've found a mysterious object while metal detecting or have some jewelry you've always wondered about, identifying what kind of metal something is can be tricky.
In this article, we'll explore 6 ways you can differentiate between precious metal and junk to definitively identify metals. These include: hallmarks; magnetism; color; weight; acid testing; and XRF spectrometer analysis.
Hallmarks are markings that are struck into the metal of rings and other jewelry. They indicate the stated purity of any precious metals, and the alleged authenticity of the item.
In the United States, there aren't any legal requirements that metals need to be hallmarked. Because of this, most jewelry made in the US does not have hallmarks.
In the United Kingdom, however, hallmarks are a regulated means of certifying purity and authenticity.
To be considered an official hallmark in the UK, Assay Offices are involved in the process. These organizations test (assay) metals to determine that the stated composition is accurate. They may use acid testing or XRF analysis to accomplish this.
For an in-depth guide to the history of hallmarking in the United Kingdom and the United States, check out this article from Lang Antiques.
Purity hallmarks tell you the stated purity (or percentage) of the specific type of metal used in the production of the jewelry. For instance, sterling silver jewelry is 92.5% pure silver, so it is hallmarked with a '925'.
Each craftsperson or manufacturer of a piece of jewelry has a maker's mark or trademark. These marks, like purity hallmarks, are stamped into the metal. They provide evidence of the person or company that created the item, and often include symbols or shapes.
Maker's marks tend to evolve over time. Having the knowledge of which mark correlates with a particular time period can help a jewelry historian or appraiser accurately date the item in question.
How to Locate Jewelry Hallmarks
- First, you'll need a magnifying glass or a jeweler's loupe.
- Rings—the hallmark is usually stamped on the inside of the band; inspect the interior surfaces with your loupe.
- Chains—the hallmarks on chains and necklaces are often located near or on the clasp.
- Bracelets—like with chains, bracelets are typically hallmarked near the clasp (if present) or on the inside of the band.
Hallmarks are not guarantees that a metal is what it claims to be. However, they provide a good starting point for identifying what you have.
Another way to tell if your jewelry -might- be made from precious metals is to test if it is magnetic.
Most metals are not magnetic. These include precious metals like gold, silver, platinum, titanium, tungsten, and palladium. However, other non-magnetic materials include some stainless steel, copper, aluminum, pewter, zinc, and non-metals like plastic.
There are comparitively few magnetic metals. Magnetic materials include iron, steel, nickel, cobalt, and rare earth metals like neodymium, samarium, and gaolinium.
How to Test for Magnetism
- Purchase a strong magnet (like this neodymium one).
- Brush the magnet across all surfaces of the jewelry.
- If the magnet sticks, it's made of steel or another ferrous (magnetic) metal.
- If it doesn't stick, your jewelry might be a precious metal. But it may also be a non-precious non-magnetic metal.
Testing for magnetism merely tells you what kind of metal you don't have. If its not magnetic, your jewelry may be a precious metal, but further testing is needed.
There are obvious and subtle differences in color that can help you differentiate types of metals.
Gold has been used in the production of jewelry, coins, and other items for thousands of years. Historically, it was revered for its lustrous sun-like yellow color. Today, gold offers a wide range of color variations that depend on its purity.
The purity of gold is measured in a unit called karats. 100% pure gold is equivalent to 24 karats. Therefore, its purity is measured in terms of how many parts per 24 are 100% pure. For example, 14k gold is 14 parts per 24, which is equivalent to 58.3% pure gold.
The higher the percentage of pure gold (and the higher the karats), the closer the metal will be to its natural yellow color. Yellow gold is alloyed (mixed) with other metals like copper, zinc, and silver. This alloying process increases the strength of the metal.
Rose gold and yellow gold have the same amount of pure gold, but the color of the former is derived from mixing in a larger percentage of copper than zinc or silver. Higher karat rose gold jewelry will appear more yellowish, as it contains more pure gold. Likewise, lower karat rose gold jewelry contains more copper, so it looks more pink.
The color of white gold is determined based on the other metals that are alloyed with the gold.
- Nickel White Gold — This is the most common white gold alloy. Nickel is used as a bleaching agent to diminish the yellow color of gold. Nickel white gold still appears slightly yellow, and is often plated with rhodium to give the surface a bright white color.
- Palladium White Gold —In this alloy, palladium is used to bleach the natural yellow color of gold. Copper and silver are added as well. These alloys are a warm grey-white, and are also sometimes plated in rhodium.
As indicated by its name, silver jewelry and coins are a grey-white color that are typically polished to a shine.
Platinum is found in nature as a grey-white colored metal. When polished, it can look similar to silver.
Like platinum, palladium is a grey-white metal. However, it's slightly darker (more on the grey side than white side of the spectrum) than platinum.
Even darker grey than palladium is tungsten, another grey-white colored metal.
Slightly darker grey than tungsten, titanium is the least white-colored of the grey-white metals.
Another way that you can distinguish between metals is by weighing them.
Precious metals (like gold, silver, and platinum) are denser than most metals. This means that they weigh more than you might expect, given their size. So, if a ring or other piece of jewelry feels light for its size, it's likely not a precious metal. It could be instead made from copper, nickel, brass, or stainless steel.
However, if it feels heavy for its size, that does not necessarily mean that it is a precious metal. Iron, for instance, is also a dense (and therefore heavy) metal. Gold or silver-plated jewelry can feel just as heavy as their precious metal-containing counterparts. These are filled with comparably dense metals to give the illusion of being genuine.
One method of weighing an unknown metal object is to measure its specific gravity. Specific gravity is a measurement of an object's size in relationship to its weight.
For example, one pound (0.45 kg) of pure gold is small enough to fit into most pockets, whereas one pound (0.45 kg) of crafting pom-poms may not fit in an entire suitcase. While they have the same weight, they take up vastly different amounts of space.
Inversely, if you weighed a one-inch (2.54 cm) cube of pure gold, and a one-inch (2.54 cm) cube of marble, you would notice that the gold outweighs the marble considerably, despite taking up the same amount of physical space.
To consistently determine the specific gravity of an object, the global standard is to compare the object's weight to the weight of an equal amount of water.
How to Measure the Specific Gravity of an Object
- First, weigh the object on a scale that is accurate to 0.01g. Note its weight.
- Then, remove the object from the scale and place a 1000ml container filled with water on the scale. Tare the scale to reset it to zero.
- Next, tie a string around the object, and gently place it into the water. For more accuracy, you can measure the weight of the string placed in the water. Our example string is 0.05 grams (0.0018 oz).
- Do not let the object touch the bottom of the container.
- Note the change in weight as the water is displaced by the object.
- For example, a silver coin that weighs 31.30 grams (1.1 oz) may displace 3.00 grams (0.11 oz) of water, meaning that it adds 3.00 grams (0.11 oz) to the weight shown on the scale.
- Now, we'll do a bit of math. Take the weight of the object from Step 1, subtract the weight of the string, and divide the result by the change in the weight of the water in Step 3.
- Using our example silver coin, we first subtract 0.05 (the weight of the string) from 3.00 (the displaced water), which equals 2.95.
- Next, we'll divide 31.30 ÷ 2.95, which equals 10.61. This is the specific gravity of our example coin.
- The full equation is included here: 31.30 ÷ (3.00 - 0.05) = 10.61
- Referencing the table below, we can see that our measurement (10.61) is closest to the specific gravity of 99.9% pure silver (10.60). So it's safe to say that our silver coin is in fact silver.
|Gold (24k Yellow)||19.32|
|Gold (22k Yellow)||18|
|Gold (18k Yellow)||15.2|
|Gold (18k White)||14.7|
|Gold (18k Rose)||15.2|
|Gold (14k Yellow)||13.2|
|Gold (14k White)||12.7|
|Gold (14k Rose)||13|
5. Acid Testing
You've checked for hallmarks, determined whether your metal has a magnetic field, evaluated for color, and measured its weight. But if you're still not sure, how can you tell if your mystery metal is a precious metal or merely plated?
Acid tests are the next step. Unlike the other methods you've tried so far, these chemicals are inherently destructive. They will damage your jewelry. However, they can help you accurately differentiate between metals by observing the reaction between the metal you're testing and the particular acid that is used.
Acid tests are also commonly referred to as touchstone tests, because you need to touch the piece of jewelry to a stone slab. They are widely used to determine the purity (or fineness) of gold jewelry.
These tests work because 24k pure gold is resistant to all but the strongest acids. So, the purer the gold you have, the stronger an acid you'll need to dissolve it. Testing solutions containing different strengths of nitric acid are available for testing 10k, 14k, 18k, and 22k gold.
A testing solution called Aqua Regia is used to test for purities between 22k and 24k. It contains a mixture of one part nitric acid and three parts hydrochloric acid.
How to Use an Acid Test on Jewelry
Things You'll Need
- Basalt or Obsidian Touchstone
- Acid Testing Kit for Gold, Silver, and Platnium
- Paper Towels
- Baking soda
- Chemical Resistant Safety Gloves
- 320-grit sandpaper or steel wool
- Put on your chemical-resistant gloves, and prepare your work area. Set out the touchstone, and select the acid dropper bottles that you will need for the type(s) of metal you're testing.
- Firmly grip the piece of jewelry, and rub it gently back and forth across the touchstone. It will leave a visible mark.
- Start with the 22k testing solution, and apply a few drops of acid to the mark. The 22k testing solution is formulated to dissolve any gold that is less than 22k or 91.6% pure, as well as dissolve any metal that is not gold.
- Wait for 30 to 40 seconds for the acid to react with the metal and neutralize.
- If the mark dissolves, it is either not gold or less than 22k gold (91.6% purity). If it is a base metal, the acid may also cause the mark to appear green.
- If the mark doesn't dissolve, we know that it is at least 22k gold.
- Wipe the touchstone with a paper towel to remove the acid.
- If the mark dissolved with the 22k testing solution, repeat this process for each of the remaining gold testing solutions. Work your way down from 22k to 18k and so on, until the mark does not dissolve.
- Apply a few drops of silver testing solution to the mark.
- Wait for 30 to 40 seconds for the acid to react with the silver.
- Fine silver (99.9% pure) will react as a bright red color.
- 92.5% pure or sterling silver reacts as a dark red color.
- 80% silver reacts as a brown color.
- 50% silver reacts with a green color.
- Silver plated items will be stripped of their plating and leave the base metal behind, reacting as an orange or yellow color.
- Wipe with a paper towel to remove the acid.
- Apply a few drops of platinum testing solution to the mark.
- Wait for 30 to 40 seconds for the testing solution to react with the platinum.
- Platinum will not dissolve, while any metal that is not platinum will be dissolved by the solution.
- Wipe with a paper towel to remove the testing solution.
Clean the Touchstone After Use:
- Remove any remaining metal from the touchstone’s surface by placing it facedown on a piece of 320-grit abrasive sandpaper or rubbing it with steel wool.
- While holding the sandpaper, apply light pressure and sand in a circular motion until your metal samples are no longer visible.
- Next, neutralize the acid by placing the touchstone in a mixture of equal parts baking soda and water.
- Rinse the touchstone in water and blot dry before storing it for later use.
6. XRF Spectrometer Analysis
Unlike acid and other chemical testing, XRF analysis is a non-destructive means of testing metals. It measures the wavelength and frequency of light, and analyses how that light interacts with a physical object.
Each element in an object reacts differently to various wavelengths of visible and invisible light.
By analyzing how the spectrum of light interacts with the object, we can identify particular elements within it.
How does an XRF spectrometer work?
An XRF spectrometer transmits X-rays into the jewelry, which excites the atoms. These excited atoms then emit light back into the spectrometer's analyzer. By analyzing the light, the spectrometer can determine the jewelry’s elemental makeup.
XRF spectrometers can be used to analyze precious metals like gold, silver, and platinum for purity. They can also identify non-precious metals, and chemical contaminants.