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Metals testing, or assaying , can tell you the precious metal used, the fineness of the alloy, and if a piece of jewelry is solid or plated. Testing can validate the stamped marks on an item of jewelry, and it is a key component of professional jewelry appraisal and estate jewelry pricing.
A low-quality, 50 percent alloy of silver and copper looks &#;silver&#; to the average consumer. This can easily lead to fraud without appropriate protection in the form of standards and testing protocols. Consumers must be confident that they are not paying 18K gold prices for 14K gold. In order to protect buyers of precious metal jewelry, a system of testing, or assaying, the quality of objects has been developed.
The assaying technologies used today are a blend of the antique and modern. The touchstone test has been used for about 2,500 years. On the other hand, X-ray technologies are a relatively new addition to our testing arsenal. Some assays are specific to a single precious metal and others can be applied to more than one with meaningful results. Tests for precious metals are described as either destructive or non-destructive. Destructive tests should be conducted with caution because they destroy at least a small part of the original object.
Several tests are described below, ranging from simple tests to more complex tests requiring special acids or equipment. The simple tests may not give you sufficient proof of the nature of your metal, but they do eliminate some possibilities and generate new areas of inquiry. If you need to be sure, ask the advice of a professional jewelry appraiser, reliable jeweler, or reputable lab.
Several of these tests may be helpful when you purchase jewelry, but the ultimate test at that time may be the price. If you think you are getting an UNBELIEVABLE deal, it probably is. Unscrupulous dealers are sometimes guilty of underkarating . Plated gold can be sold as karat gold. Rhodium plating can disguise jewelry that is constructed of both platinum and white gold. Know your jeweler, learn to ask appropriate questions, and avoid hasty decisions.
Key examples of the types of precious metal testing used to determine authenticity and quality are explained below.
Color Test
Heft Test
Magnetism Test
Electronic Testers
Touchstone Test
Acid Testing
Fire Assay
Torch Test
X-Ray Metal Analyzers
Atomic Absorption Spectrophotometry
Study the color of your jewelry; you can learn many things, which will direct you to other tests that provide proof of the nature of the metals.
First, observe whether the color is evenly distributed or if it is patchy. Look especially around hinges or clasps for signs of discoloration or wear. Plated gold pieces may have areas where the gold has rubbed off and the base metal shows through.
Yellow gold shouldn&#;t have a coppery or brassy color. White gold and platinum can often be distinguished, because white gold may have a very slight yellowish tint unless it has been plated with rhodium. Silver may tarnish, but platinum never does.
This is another easy test. Carefully toss or bounce the object in the palm of your hand. If it feels very lightweight, and it is a solid&#;not hollow&#;piece, then it is unlikely to be made of precious metal. One of the characteristics of precious metals is that they feel very solid and weighty. This is especially true of platinum and gold.
If your jewelry is hollow, it may be difficult to use this test. Electroformed pieces are hollow because of the way they are manufactured.
The Heft test is related to the specific gravity of the metal. The specific gravity of a material is the ratio of its weight to the weight of an equal volume of water. The specific gravity of pure platinum is 21.40, which means it is 21.4 times heavier than water. Pure gold has a specific gravity of 19.36, and silver 10.53.
The specific gravity of copper, nickel, brass, iron, and stainless steel are all below 9. This illustrates why base metals will feel lighter than precious metals. This is also why pure gold, for example, will feel heavier than gold alloys, which are mixtures of gold and base metals. This is also why a platinum piece will feel twice as heavy as the same piece in silver.
This is an easy test. Simply hold a magnet to your jewelry and check for attraction. Make sure your magnet is strong enough to provide reliable results. Good magnets can be purchased at most toy or hardware stores. Your refrigerator magnets are not likely to be strong enough to produce reliable results.
Gold and most platinum alloys are not magnetic, but plated goods with a base metal foundation of iron or stainless steel will be. Remember that cobalt-platinum alloys are slightly magnetic.
The Magnetism Test can provide a quick means to separate gold plated jewelry from jewelry made of karat gold. It can also separate platinum alloys lacking cobalt from ones with cobalt, which can be slightly magnetic.
Electronic testers are a fast and easy means for detecting the fineness of your gold jewelry. They are variably priced and available at jewelry supply stores. While testers can be accurate within two karats, they cannot tell you if your piece is gold plated because they only perform a surface contact test.
You can get a deeper reading by nicking your jewelry in an inconspicuous spot and taking a reading, but this is not recommended for obvious reasons. Electronic testers are easy to use, portable, and give quick results, but some may leave a small mark on items with low karatage.
This ancient test is used primarily for determining the fineness of gold alloys. The touchstone test requires the use of a black basalt slab called a touchstone, nitric and hydrochloric acids, and a set of test or comparison needles with a range of precious metal finenesses. The unknown, or the metal to be tested, is rubbed on the stone leaving a streak. Never rub prongs or visible parts of a piece of jewelry on the touchstone. Always choose an area of the piece that does not show. Additional streaks are then made using the test or comparison needles; one with an estimated fineness equivalent to the unknown metal and at least two others estimated to be of lower and higher fineness than the unknown.
The color of the streaks is compared briefly and then acids are applied to see the reaction. Higher karat gold will require the use of aqua regia. Nitric acid may be used alone for 14K and lower karat gold alloys. Compare the reactions of the unknown metal with that of the test needles. Watch for color changes and watch to see how quickly the streaks disappear. When two streaks react the same way, they have the same fineness.
The touchstone test is not suitable for gold filled or gold plated items. It can detect fineness of ten to twenty parts per thousand, but it does not work as well with higher karat alloys and white golds. Silver can be assayed with a touchstone, but some expertise is required because the metal used to alloy the silver can affect the results.
Although the touchstone method can work with platinum, it is a challenging procedure best left to professional assayers. There is no sure touchstone test for other platinum group metals.
Touchstone testing must be done with care to get accurate results. If your results are not accurate try some of the following:
Make sure your acids are not stale or contaminated.
Make sure your test or comparison needles are not corroded. They should not be stored with the acids.
Do not use the same side of the touchstone for testing high and low karat gold.
Make sure your streaks have the same width and intensity.
Make sure to test all parts of a piece of jewelry. Sometimes the item can be made of component parts with different finenesses.
Remember that is important to take precautions when using, storing and disposing acids. More information is provided in the section below on Acid Testing, but amateurs should be trained in the proper techniques before attempting these tests.
When you want to get to the truth of a matter, as the expression goes, you &#;apply the acid test.&#; This age old expression refers to ancient techniques we still employ for determining the quality of precious metals.
Acid testing is an extension of the touchstone test. It can be destructive to your jewelry so it must be practiced with care. There are also very real human hazards, so you must thoroughly research the topic if you decide you&#;d like to try it. At a minimum, you should always avoid breathing the fumes and wear gloves and protective eyeglasses when working with acids. Acids also require specific mixing, storage, and disposal protocols beyond the scope of this webpage. The layman can apply acid tests, but only when they are properly trained. In most cases, it would be best to have a professional do these tests for you.
One of the characteristics of precious metals is their resistance to chemicals. Standard acid tests for gold and platinum are based on the fact that they will not react with pure nitric acid but they will react to aqua regia, which is a mixture of nitric acid and hydrochloric acid.
It is possible to purchase acid testing liquids at jewelry supply stores or rock shops. If for example, you purchase a small bottle of 14K gold testing liquid (nitric acid) and place a drop on an inconspicuous part of your jewelry, you can observe the following reactions:
18K+ gold no change
14K gold no change or only slight brown color change
10K gold turns brown
Low karat gold turns brown or green
Brass, copper, nickel turns green
Platinum no change
Silver turns white or gray
Stainless steel (usually) no change
If the spot bubbles or hisses your piece is definitely not gold or platinum. Lower karat gold may slightly effervesce, but it will not bubble and hiss. Brown and green color change is due to the base metals in the gold alloy. Silver is easily distinguished from quality white gold. If you have trouble noting the color change, you can blot the spot with a white napkin or paper towel and look for the color change on the white background.
If you are testing a piece that is 10K or less, the acid can leave a permanent brown stain. If you have reason to believe that your piece is gold plated, it would be necessary to nick or file the surface of your jewelry in an inconspicuous area to spot test below the surface. The reactions will be the same as those listed above; note any bubbling, hissing, and color change.
If you have purchased a platinum testing acid (aqua regia) for a silver-colored piece, you may observe the following reactions:
Platinum no change
Nickel white gold turns yellow
Palladium white gold turns brown
White base metal turns green
Silver is tested with Schwerter's solution . When a drop is applied to your jewelry, you may observe the following reactions:
Pure silver bright red
Sterling silver dark red
Lower % of silver dark red to dark browns and greens
Nickel blue-green
Lead yellow
The reactions may vary a bit depending on the silver alloy. As with gold plated objects, if you believe that your jewelry may be silver filled or silver plated, make a small nick or file the surface to expose the metal under-layer and repeat the test.
After testing with acids, make sure you neutralize the reaction by dipping the jewelry in a solution of water and baking soda. Then carefully rinse the piece with fresh water. Make sure you do not get any acid on gemstones and store and dispose of all materials properly.
Contact us to discuss your requirements of Pure Metal. Our experienced sales team can help you identify the options that best suit your needs.
Fire assay, or cupellation, is an extremely accurate means of determining the fineness of gold. Although it is a destructive and time-consuming test, assayers have used it for centuries. A tiny sliver of metal, typically about 250 milligrams, is removed from the jewelry to be tested and carefully weighed. It is then wrapped in lead foil along with a piece of silver.
The entire package is placed in a cupel and heated in a furnace. The lead melts, oxidizes, and dissolves out the base metal, which is absorbed into the cupel itself. What remains is a bead or button of gold and silver.
The bead is then treated with nitric acid to separate the silver from the gold&#;a process called parting . The gold portion is weighed and when its weight is compared with the weight of the original sliver, the fineness of the jewelry can be determined. The fire assay method has an accuracy of two to three parts per ten thousand!
This is a destructive test that will confirm if a sample is made of platinum. A tiny sliver of metal is removed from the jewelry from an inconspicuous area. The silver is subjected to intense heat from a hot flame.
If the metal melts and forms a ball, it is not platinum. Platinum has an extremely high melting point, so with this kind of flame, platinum will retain its shape but begin to glow red-hot.
New X-ray technologies (including x-ray fluorescence) are being used to identify the fineness of precious metal objects. They are also capable of identifying the metals used to make the gold, platinum and silver alloys. The process is fast and non-destructive, but slightly less accurate than the fire assay. However, much of the equipment is expensive and available only in specially equipped laboratories.
New developments in the market include similar instruments, such as the X-tester, which are more reasonably priced. A major retailer in India has been using this device to enhance consumer confidence. As items are sold, they are tested and certified as a guarantee of the fineness of the gold.
Detecting fineness is more difficult in platinum than in other precious metals. It is usually left to highly skilled professionals who have access to special equipment. Atomic absorption spectrophotometers analyze the chemical composition of materials. The test is destructive because it requires a small sample of platinum from your jewelry.
The platinum is dissolved in solution and then vaporized in the spectrophotometer. The reading from your sample will be compared with that of other samples containing known concentrations of platinum. This technique can also be used on gold and silver if necessary.
Now that we have completed the breakdown of precious metals testing, a brief overview of the Precious Metals Glossary | Definitions of Precious Metals Terminology would be helpful to cover any remaining questions about terminology.
Q235 and Q345 are 16 Mn steel grade with good formability and weldability properties. It&#;s commonly used for structural applications and parts for a variety of industries. Q345 offers better performance at low temperatures and offers better steel strength.
Hot rolled steel is produced when steel is processed by a series of roll presses at temperatures over °F. The process creates a steel that is easily formed or shaped into large pieces and is best used where tolerances aren&#;t as important.
Sheet metal is made from a variety of metals that each have their own unique properties and offer unique benefits. A list of the most common sheet metal materials used for fabrication have been summarized below.
The sheet metal used in your sheet meetal fabrication includes a very broad list of possible materials . Making the best choice for your products includes decisions about the type of metal, its thickness, and a choice of form. What you choose should be based on your overall expectations, desired end product, and recommendations from your sheet metal fabricator contractor manufacturing services
Section 3
Cold rolled steel (CRS) is essentially hot rolled steel that has gone through an additional rolling process at room temperature.
This additional processing produces a steel with closer tolerances and a broader range of finishes. The result is an increase in strength by as much as 20% compared to hot rolled steel. SPCC is commonly used for automotive parts and some construction applications. SPCC can be used for galvanized products, appliances, containers, and other products.
SAPH440 is commonly used for automotive frames, wheels, and other parts. It has very good tensile strength making it a good choice for load bearing or structural uses.
Advantages:
Disadvantages:
Commonly used for:
Section 4
The category of spring steel includes several high yield strength steels including low-alloy manganese, medium-carbon steel, or high-carbon steel. They are primarily used to manufacture springs as the steel will return to its original shape after twisting or load bearing.
A carbon steel can be used for small springs, but large springs are best when an alloy is used. High carbon spring steel is a common choice, inexpensive, and easily processed. It is not suited to extreme temperatures or for shock/ impact loads. Alloy spring steel are well suited to shock or impact loads or conditions with high stress. Stainless spring steel can be used in some forms at extremely high temperatures (288°C) and are corrosion resistant. 65Mn is a high carbon with manganese to improve hardenability. It has good wear resistance and good workability.
Advantages
Disadvantages
Commonly used for:
Section 5
Aluminum is a pure metal that is easily alloyed with small amounts of other materials like copper, manganese, silicone, or magnesium. It is not magnetic or combustible and is a good conductor of electricity. Aluminum offers good corrosion resistance and is generally easy to form and process. It comes in several different grades and is often used because of its weight. It weighs about 1/3 of other materials like iron, steel, copper, and brass. It conducts heat well and is non-toxic making it a good choice in a variety of applications.
AL is a wrought alloy with high electrical conductivity, corrosion resistance, and workability but somewhat low mechanical strength. It&#;s commonly used in electrical and chemical industries. AL is most often used for architectural applications or trimming. It has high tensile properties and offers good finish options. It also offers high corrosion resistance and is a good option for anodized applications. AL is the most flexible heat-treated alloy with excellent workability. It&#;s well suited to most processes and has good corrosion resistance. AL is the highest strength non-heat-treated aluminum alloy and offers very good fatigue resistance. Highly workable, AL can be formed into complex shapes and offers good saltwater corrosion resistance.
Advantages
Disadvantages
Commonly used for:
Section 6
Stainless steel includes a variety of sheet metals which contain at least 10.5% chromium. There are many different grades available, offering corrosion resistant and a commercially familiar appearance. Standard or austenitic stainless steel (300 series steels) is very common and does not require heat during the manufacturing process. They offer good corrosion resistance, formability, and weldability.
SS301 has high work hardening and is commonly used for trailer bodies and fasteners. SS304 has low carbon, is an economical grade but is not seawater resistant. SS316 has higher molybdenum content that improves its resistance to seawater corrosion. A lower carbon version (SS316L) is available for better corrosion resistance after welding.
Advantages
Disadvantages
Commonly used for:
Section 7
Cold galvanized steel has a zinc coating painted to the steel surface to protect it from corrosion. The coating will provide both a barrier protection and a galvanic protection to help extend the life of the product. It can be applied with brushes, rollers, sprayers, or through electro galvanizing. The paint includes special binders so it will mechanically bond to the steel. SGCCis a galvanized steel with good weldability and formability. It can have a pure zinc coating or have a Zn/Fe alloy coating.
Advantages
Disasdvantages
Commonly used for:
Section 8
Each metal has its own unique characteristics. This section of our guide outlines some of the factors that you should consider when making your choice of materials.
Surface finish Yield Tensile Hardness GB Standard Powder coating E-coating Zinc plating Dacromet Anodized Passivation Cold Rolled Steel (CRS) SPCC X X X X &#;210MPa &#;350MPa HB 65 - 85 JIS G- SAPH440 X X X X &#;305MPa &#;440MPa HB 80 ±30 Q/BQB 310- Hot Rolled Steel Q235 X X X X &#;235MPa 375 ~500MPa HB 120 ±40 GB/T 700- Q345 X X X X &#;345MPa 490 ~675MPa HB 120 ±40 GB/T - Spring Steel 65Mn X X &#;785MPa &#;980MPa HB 190 - 340 GB/T - Aluminium AL X X &#;35MPa &#;75MPa HB 26 ±5 GB/T - AL T6 X X &#;276MPa &#;260MPa HV 15 ~ 18 GB/T - AL T5 X X &#;170MPa &#;250MPa HB 25 ±5 GB/T - AL H32 X X &#;70MPa 210 ~ 260MPa HV 11 ±2 GB/T - Stainless SS301 X X &#;205MPa &#;520MPa HB 76 ~ 187 GB/T - SS304 X X &#;205MPa &#;520MPa HB 76 ~ 187 GB/T - SS316 X X &#;205MPa &#;520MPa HB 76 ~ 187 GB/T - Cold Galvanized Steel SGCC X &#;200MPa &#;380MPa HB 50 - 65 JIS-G
Section 9
Different metals can accommodate different surface finishes. Some will require additional processing before a surface finish can be applied. Your choice of surface finishes can be for aesthetic or functional reasons &#; or both.
Section 10
The yield strength of a metal is the point at which applied stress will cause it to deform and not return to its original shape. It provides an indication of a metal&#;s elasticity and the maximum force you can apply to it before it will permanently deform, buckle, or even fail. Processes like annealing can impact the yield strength of some materials.
Section 11
Hardness refers to the metal&#;s ability to resist deformation from an impact, abrasion, or load. You can measure hardness based on its resistance to scratches, indentations, or rebounds. Some issues with hardness can be overcome with a hardening process. Hardness is important for load bearing structures as hard metals are better able to withstand the application of load or abrasion.
Section 12
Tensile strength refers to ability of a metal to resist force. Higher tensile strength requires more force to snap it for example. If the product you&#;re producing doesn&#;t need to bear any load, then a metal with less tensile strength might be the best choice. Keep in mind that how you form the sheet metal can impact its strength and the load it can bear.
Section 13
The ductility of a metal offers insight into how pliable it is and how easy it is to form. When a metal is referred to as having high ductility, that means it easier to form and bend.
Section 14
If your product requires welding, it&#;s important to understand how easy or difficult a metal is to weld. Some metals require extensive preparation or advanced welding techniques which can impact both your budget and schedule.
Section 15
A metal that has high machinability is one that can be more easily cut and cut at higher speeds. Hard machinability requires more power and time to cut the metal.
Section 16
The material you choose should take into consideration the environment it will be exposed to. Some metals respond better than others to factors like water, oxidation, or other elements it will be exposed to. Some metals, like stainless steel, won&#;t corrode but they can develop an oxide film. Also keep in mind that galvanic corrosion can occur when to dissimilar metals are in contact with each other.
Section 17
Choosing a lighter weight material might be best for large objects or objects that need to move (like vehicles, trailers, etc.). At the same time, you need to consider the strength of the material. In general, lighter metals have less strength than heavier ones &#; although that&#;s not always the case.
Section 18
Cost usually isn&#;t&#; the most important factor in choosing a sheet metal for fabrication. It&#;s important to make the best choice based on the other factors we&#;ve listed. However, if there is an equally good alternative that has a lower cost, it&#;s worth considering. Keep in mind however, sometimes lower cost materials require additional processing which may result in you not actually saving a lot had you used the higher cost material instead.
Our team of engineers and technicians here at Komaspec have more than 15-years&#; experience in sheet metal fabrication in China and are glad to review your product design together and help you select the fabrication process that best suits your product&#;s needs, whether it&#;s laser cutting, bending, stamping, etc..
For more information, please visit INvar Material.