Simple field checks, gram-scale testing, and specific gravity for detectorists

One of the first questions a new detectorist asks after recovering an unusual ring, buckle, button, coin or piece of jewelry is, “What metal is this?” Color alone is not enough. Soil staining, corrosion, plating and age can make one metal resemble another. The best approach is to use several simple clues together, beginning with tests that do not damage the find.

A good rule is simple: do not aggressively clean, scratch, file or chemically test a potentially valuable or historical object until you have first examined it carefully. A collectible coin, military artifact, old button or piece of antique jewelry can lose value through unnecessary testing or cleaning.

Start With the Easy Field Checks

Magnet. A small neodymium magnet is useful for eliminating possibilities. Gold, silver, copper and brass are not strongly magnetic. If the entire object strongly sticks to a magnet, it probably contains iron or steel. If it does not stick, that does not prove it is precious metal because aluminum, lead, zinc and many other metals are also nonmagnetic. If only a clasp, spring or pin is attracted, the main body of the jewelry may still be made from another metal.

Color and Patina. Silver often develops gray or black tarnish. Copper begins reddish or orange and commonly ages to brown or green. Brass is normally yellow-gold when fresh but can become brown or green in the ground. Gold usually retains a gold-colored appearance, although white gold and rose gold are intentionally alloyed to different colors. Patina is simply the surface change that develops as metal reacts with air, moisture and soil over time.

Patina type	What it looks like	Metals it commonly suggests	Examples
Green / verdigris	Green, blue-green, turquoise	Copper, bronze, brass	Kettle point, old brass buttons
Dark brown / chocolate	Brown to nearly black	Brass, bronze, copper	Military buttons, buckles
Red-brown rust	Orange, reddish brown, flaky	Iron, steel	Victorian valve/iron relics
Black / gray silver toning	Gray, charcoal, black	Silver	Silver coins, sterling rings
White / gray oxidation	Chalky white, pale gray	Lead, pewter, zinc	Bullets, hem weights
Gilt + patina	Gold patches with brown/green underneath	Gilded brass/copper	Ohio gilded eagle relic

Hallmarks. Use a 10-power loupe and look inside rings, on clasps, on the backs of pendants and in protected areas. Common silver marks include 925 and STERLING. Common gold marks include 10K, 14K and 18K, or the corresponding fineness marks 417, 585 and 750. A hallmark is a strong clue, but it is not absolute proof because plated and counterfeit items can also carry marks.

Existing Wear. Before making a new scratch, inspect worn corners, old scratches, and attachment points. If a yellow surface reveals reddish copper underneath, plating is likely. If a silver-colored surface reveals yellow brass underneath, the piece may be silver plated. Let existing damage tell you what it can before creating any new damage.

What Kind of Scale Should a Detectorist Use?

Use Grams. For coins, rings and small metal finds, grams are the simplest and most useful unit. For the average detectorist, a compact digital jewelry or pocket scale with a capacity of about 200 to 500grams and a readability of 0.01 gram is an excellent choice. It is precise enough for coin-weight checks, jewelry weights and most routine comparisons.

Look for Four Features: a 0.01g readout, a tare/zero button, a calibration function, and an included calibration weight. A flat stainless weighing platform and a protective cover are also useful. Calibrate the scale according to its instructions and place it on a firm, level surface away from vibration or moving air.

For Specific Gravity, 0.001g Can Be Better. A 0.01 g scale can give a useful specific-gravity estimate on a reasonably heavy solid ring or other object, but very small jewelry displaces only a tiny amount of water. For rings, earrings, and other light pieces, a 0.001 g milligram scale provides a noticeably better measurement. A practical setup is therefore a 500 g × 0.01 g scale for everyday detector work and, if you become serious about specific-gravity testing, a smaller 50 or 100 g × 0.001 g scale for precision work.

Specific Gravity: A Powerful Home Check

Specific gravity (SG) is a comparison of an object’s density with the density of water. In plain language, it tells you how heavy a metal is for the amount of space it occupies. Because gold is very dense, a solid gold item will normally have a much higher specific gravity than brass, copper, or aluminum.

A Beginner-friendly Method Uses the Gram Scale and a Cup of Water:

1. Weigh the clean, dry object in air and record the weight in grams.
2. Place a cup of water on the scale and press TARE or ZERO so the display returns to 0.00 g.
3. Suspend the object completely under the water with very fine thread or wire. Do not let it touch the bottom or sides of the cup, and remove any trapped air bubbles.
4. Record the new reading on the scale. That reading represents the mass of the water displaced by the object.
5. Divide the dry weight of the object by the displaced-water reading. The result is the approximate specific gravity.

Example: If a solid ring weighs 6.50 g in air and produces a 0.50 g reading when suspended in the tared water, 6.50 ÷ 0.50 = 13.0. That reading would be close to the published specific gravity of many 14K yellow-gold alloys.

Important: Rings With Stones and Mixed Construction

The specific-gravity formula still calculates the density of the entire object, but it cannot isolate the gold in a ring that contains stones or other materials. A diamond, gemstone, enamel, solder, steel spring, or other component contributes its own weight and volume to the measurement. Because most gemstones are much less dense than gold, a stone-set gold ring will often produce a lower specific-gravity reading than the gold alloy itself and may appear to be a lower karat than it really is. For that reason, do not compare the SG of a stone-set ring directly with the gold-karat values in the chart below. Specific gravity is most useful for plain, solid, single-metal pieces with no stones, hollow spaces, or mixed-metal construction.

Approximate Specific Gravity Reference

Gold alloys do not all have the same specific gravity. The metals mixed with the gold change the density, which is why yellow, white, red, and green gold of the same karat can read differently. The following published jewelry-reference values are useful guides:

Metal / Alloy	Approx. SG	Metal / Alloy	Approx. SG
Aluminum	2.70	14K white gold	12.61
Brass	8.40	14K yellow gold	13.07
Copper	8.94	14K red gold	13.26
Sterling silver	10.40	14K green gold	14.20
Pure silver	10.53	18K white gold	14.64
10K green gold	11.03	18K red gold	15.18
10K white gold	11.07	18K yellow gold	15.58
10K yellow gold	11.57	18K green gold	15.90
10K red gold	11.59	24K gold	19.36

Do not treat the number as proof of karat. Specific gravity works best on a plain, solid, single-metal object. The formula remains mathematically valid for a ring with stones, but the result is the combined density of the entire ring, not the density of the gold alone. Stones, hollow construction, solder, enamel, trapped air, heavy corrosion, mixed-metal parts and plating can change the reading. Use the chart only as a guide for suitable solid pieces, and combine SG with hallmarks, appearance, weight and other testing.

Why the Same Scale Is Useful for Coins

A 0.01g scale also helps with recovered U.S. coins. For example, the U.S. Mint lists the modern cent at 2.50g, nickel at 5.00 g, dime at 2.268g, quarter at 5.67g and half dollar at 11.34g. Older silver issues have different standard weights. Wear, corrosion, and adhering soil can alter the weight slightly, so coin weight should also be treated as a comparison rather than a stand-alone verdict.

Recommended Digital Scales for Metal Detecting Finds

The scales shown below are examples of models that match the accuracy and features discussed in this guide. They are provided to help readers compare suitable options and are not paid endorsements. Product specifications, pricing, sellers, and availability may change, so we recommend confirming the current details with the retailer or manufacturer before purchasing.

Affiliate Disclosure: Some links in this section are affiliate links. If you make a qualifying purchase through one of these links, Focus Speed may earn a small commission at no additional cost to you. These commissions help cover the costs of operating Focus Speed, including website hosting, research, content development, and maintaining free educational resources for the metal detecting community. Affiliate relationships do not influence the information, comparisons, or recommendations provided in this article.

The Best Beginner Rule

Never let one test convince you that a find is gold or silver. A strong identification comes from several clues agreeing with one another: the magnet response, color and patina, hallmark, visible wear, gram weight and, when appropriate, specific gravity. The more independent clues that point in the same direction, the more confidence you can have before moving on to professional acid testing, electronic testing, or appraisal.

References

Specific-gravity values: Stuller, “Where can I find the specific gravity of various materials?”
Current U.S. coin specifications: United States Mint, Coin Specifications