Common Metal Identification Methods
The ability to identify metal is a valuable skill for many operations such as welding, machining, cutting, and fabricating.
A number of field identification methods can be used to identify a piece of metal. Some common methods are surface appearance, spark test, chip test, the magnet test, and occasionally a hardness test. Sometimes you can identify a metal simply by its surface appearance.
Metalworkers use various methods, from traditional to modern ones, to identify the scraps and sheets of metals that come into the shop. In this post, we will explore some well-known traditional and modern metal Identification methods as well as the pros and cons of using them.
Traditional Testing Method
Some popular traditional testing methods are Appearance, Spark, Rockwell, and Brinell Hardness. Generally, the benefit of these tests is that they are cost-efficiency, but the disadvantages include the strong dependency on personnel experience and the methods that could damage the samples.
1. Appearance Test
The appearance test does not always provide sufficient information, but it could provide enough information to classify the metal. This test considers the color of metal and the existence of a machined mark or lack of one on the surfaces of the metal.
2. Spark Test
A spark test is conducted by allowing a piece of metal to touch the high-speed portable or stationary grinder with enough pressure to create a spark of the stream. An experienced metal worker visually inspects the spark stream to identify the metals and considers the length, color, and form of the spark stream before identifying the metal.
When using this visual spark testing technique, we recommend reserving this test to experienced technicians.
3. Rockwell Test
A Rockwell hardness-testing machine is needed to perform this test. The point of this method is to measure the depth of an indentation made by a cone-shaped point in the testing machine.
This specific test is limited as it reveals only one of many metal properties – which is the hardness of the metal. Soft metals will have deeper indentations and hard metals will have lighter impressions.
4. Brinell Hardness Test
Brinell hardness test is similar to the Rockwell as they both evaluate the metal impression left by an intended object. The Brinell hardness test is different in that it measures the area of impression.
A harden ball is forced onto the metal surface under a 3,000 kg load to create an impression. The impressed area is then measured and given a hardness number. A large impressed area indicates softer metal, which means a lower hardness number.
Modern Metal Testing Methods
No longer relying on just the eye or the personal experience, modern metal testing methods incorporate technology to improve the processing speed and result in accuracy while protecting the samples.
One popular technique is called the Positive Metal Identification (PMI) that uses X-ray Fluorescence (XRF) and Optical Emission Spectrometry (OES). PMI is the analysis of metallic alloy to establish its composition and alloy grade identification by reading the quantities by percentage of its elements. PMI analyzers provide detailed element analysis of materials for uses from industrial to research.
Both XRF and OES techniques are widely used in the industry because they provide accurate results within seconds of testing. There are slight differences in the techniques as explained below.
1. Optical Emission Spectrometry
Optical Emission Spectrometry (OES), is easy to use, fast, and can define the exact quantitative breakdown of solid materials. OES, also known as Atomic Emission Spectrometry uses the intensity of light emitted at a particular wavelength to determine the elemental composition of a sample. Like fingerprints, the emission of rays and light are unique to metal types.
An analysis is given as a percentage breakdown. OES analysis is versatile and can be used with stationary, portable, or mobile environments. Combining the speed, versatility, and easy-to-use of this method, make it the ideal test for alloys.
2. X-Ray Fluorescence
X-Ray Fluorescence (XRF) is a highly precise and accurate measure of the elemental composition of materials. XRF spectrometers excite a sample with high-energy X-rays forcing the sample to emit certain characteristic rays which are read by the XRF spectrometer.
A handheld XRF gun is required, but the process can occur is fractions of a second. Metals with high percentage levels can make a few seconds to be read, while metals with part-per-million levels can take up to a few minutes. Still, you cannot find a faster reading.
3. X-Ray Diffraction
X-Ray Diffraction (XRD) is used to identify the chemical composition information of metals. XRD can be used hand in hand with XRF as XRD takes the testing one step further to give added context.
The process identifies the crystalline phases present and compares them to a database of archived phases. Elements are analyzed in a ground powder form.
XRD helps evaluate minerals, polymers, corrosive products as well as other varying unknown materials. This method can be useful to identify and quantify phases as well as doing texture analysis.
Unlike traditional methods where it takes years of training, metal workers armed with PMI spectrometers can be trained and begin working on their assignments in minutes.
For new and used metal analyzers that use this technology, check out our online inventory of metal analyzers.
4. Laser-Induced Breakdown Spectrometer (Libs)
Laser-induced breakdown spectrometer (LIBS) is a form of Atomic Emission Spectrometry but it uses a highly energetic laser pulse to excite the sample. This technique is also considered non-destructive to samples and is popular in scrap metal analysis.
Visually Identifying Common Metals
Ferrous or Nonferrous?
Ferrous means that the metal has iron content which in most cases makes it magnetic and nonferrous means it doesn’t have iron in it. An example of ferrous metal is mild steel, also known as low carbon steel. An example of a nonferrous metal is copper or aluminum. It’s always a good idea to bring a magnet to the scrap yard.
Aluminum is a shiny grey metal and has a clear oxide that forms in contact with air. This may not be the best thing for identifying it, but the aluminum melting point is 658° C (1217°F). Also, aluminum is non-sparking. Aluminum’s density is 2.70 g/cm3, this is a good way to identify it because you can find the density of a material by density = mass ÷ volume. As I said earlier, aluminum is nonferrous.
Most bronze is an alloy of copper and tin, but architectural bronze actually has a small amount of lead in it. Bronze has a dark coppery color and gets a green oxide over a period of time. bronze’s melting point is 850-1000°C (1562-1832°F) depending on how much of each metal is in it. Bronze is nonferrous. Because bronze is an alloy density vary. Bronze vibrates like a bell when hit.
Brass is another copper alloy but it has zinc instead of tin. Brass has a yellow gold color. Brass’ melting point is 900-940°C (1652-1724°F) depending on how much of each metal they used. Brass is nonferrous. Because brass is an alloy its density varies. If hit brass vibrates like a bell, this can be used to determine if something is brass instead of gold.
Chromium is a very shiny silver color and forms a clear oxide over time. Chromium melting point is 1615°C (3034°F). Things are rarely made of pure chromium but lots of things are coated with it to make it shiny and not rust. Chromium density is 7.2 g/cm3. Chromium is nonferrous.
Copper is made into many alloys like brass and bronze. Copper is light red in color and gets a green oxide over time. Copper is nonferrous. The copper melting point is 1083°C (1981°F). Coppers density is 8.94 g/cm3. Copper, like brass, also vibrates like a bell when hit.
Gold is a shiny yellow color and does not have an oxide. Gold’s melting point is 1064.18°C (1947.52°F). Gold is very soft and is very heavy. Gold has high electrical conductivity (more electricity can pass through it) which means that the connectors on many cords have gold plating. Gold’s density is 19.30 g/cm^3. Gold is nonferrous. Gold is a “precious” metal which means that it is very expensive and is used in coins and jewelry.
Iron is ferrous (finally!) and magnetic. Iron is a dull grey when unpolished and its rust is a reddish color. Iron is also used in a lot of alloys like steel. Irons melting point is 1530°C (2786°F). Irons density is 7.87 g/cm3.
Lead is a dull grey when unpolished but shinier when polished. Lead has a relatively low melting point, 327°C (621°F). Lead is nonferrous. Leads are very heavy; their density is 10.6 g/cm3.
Magnesium has a grey color and develops an oxide that dulls the color. Magnesium’s melting point is 650°C (1202°F). Magnesium is extremely flammable in powder or thin strips. Magnesium burns very brightly and is very hard to put out because it is so hot that if you throw water on it, it separates it into hydrogen and oxygen, two very flammable gasses.
Magnesium can also burn without oxygen making it even harder to put out. Magnesium is very light with a density of 1.738 g/cm^3. Because magnesium is so light it is used in engine blocks in cars, and because it burns so brightly it is used in incendiary weaponry (to incinerate things) and fireworks.
Mild steel is black to dark grey unpolished and silvery polished. Mild steel has the same red rust oxide as iron. Mild steel is also ferrous and magnetic. Another name for mild steel is low-carbon steel.
Mild steel makes yellow sparks when ground down. Mild steels density is about 7.86 g/cm3but it varies since it is an alloy of iron and carbon (low carbon steel). The mild steel melting point is 1350-1530°C (2462-2786°F).
Nickel is shiny silver when polished and is darker unpolished. Nickel is one of the few metals that is not an iron alloy that is magnetic (5¢ US nickels are not magnetic because there made of a copper-nickel alloy). The nickel melting point is 1452°C (2645°F). Nickels density is 8.902 g/cm3.
Stainless steel is a shiny silver color and does not form an oxide. Chromium (step5) is mixed into the steel, when it hardens the chromium leaves a coating of its oxide on top of the steel, this is too thin to see so the steel’s color shows through.
Stainless steels melting point is from 1400-1450 °C (2552-2642 °F). Stainless steels density varies because it is an alloy. Depending on the alloy some stainless steels are magnetic, but all are ferrous.
Tin is silvery grey in color (like most metals) when polished and darker when unpolished. Tin has a comparatively low melting point of 231°C (449°F). Tins density is 7.365 g/cm3. Tin is nonferrous
Titanium is a silvery-grey metal when unpolished and darker when unpolished. Titanium gives off bright white sparks when it is ground. Titanium is nonferrous. The titanium melting point is 1795°C (3263°F). Titanium density is 4.506 g/cm3.
Silver is a shiny grey even before being polished but develops a black film over time and has to be polished. Silvers’s melting point is 961.78°C (1763.2°F). Silver has the highest electrical conductivity (more electricity can pass through it) than any other metal.
Silvers’s density is 10.49 g/cm^3. Silver is nonferrous. Silver is a “precious” metal meaning that it is expensive and is used in coins and jewelry.
Zinc is naturally dull grey and is very hard to polish. Zinc has an oxide that flakes off carrying some of the zinc so other things are coated in it so the zinc “rusts” instead of the base metal, this is called galvanization.
Because of its low cost zinc is the main metal in us pennies. Zincs melting point is 419°C (786°F). Zinc is nonferrous. Zincs density is 7.14 g/cm3.