Blue Amber Specific Gravity — How to Test and What It Means

Blue amber specific gravity measures 1.05–1.10 — only 5–10% denser than water. This enables the saltwater float test: dissolve maximum table salt in warm water, drop the specimen in, and genuine amber floats while most plastics and all glass sink. The test is non-destructive, requires no equipment, and takes under 60 seconds. Copal also floats (similar SG) so pair with the acetone test for complete authentication.

What Specific Gravity Means for Blue Amber

Specific gravity is the ratio of a material's density to water's density. Water has SG 1.00 by definition. Blue amber's SG of 1.05–1.10 means a given volume of amber weighs only 5–10% more than the same volume of water. This is remarkably light for any gem material — most mineral gems have SG values between 2.5 and 4.5.

This lightness has practical consequences beyond testing. Large blue amber pendants weigh very little compared to stone jewellery of the same size. A statement necklace with a 30-gram amber centrepiece feels featherlight on the neck. An amber bracelet with substantial beads causes no wrist fatigue. The full physical properties guide covers how SG affects wearability in jewellery applications.

The SG value is consistent across all amber origins — Dominican, Sumatran, and Mexican blue amber all fall within the same 1.05–1.10 range because the fundamental cross-linked polymer chemistry of fossilised resin produces the same density regardless of source tree or geographic location.

The Saltwater Float Test: Step by Step

The saltwater float test — recommended by the International Gem Society — exploits the fact that amber's SG sits between fresh water (1.00) and saturated saltwater (approximately 1.13). Amber sinks in fresh water but floats in saltwater. Most common imitation materials have SG values well above 1.13 and sink in both.

Materials needed: Table salt (standard cooking salt — iodised or plain, both work), warm water, and a glass or clear container tall enough that the specimen can float without touching the bottom or resting against the sides.

Preparation: Fill the container with approximately 300ml of warm water (warm dissolves salt faster). Add table salt — approximately 7–8 tablespoons for 300ml. Stir vigorously until the salt is fully dissolved. The water should taste intensely salty. If undissolved salt remains at the bottom after stirring, you have reached saturation — which is what you want.

Testing: Gently place the specimen into the saltwater. Do not drop it — lower it in. Genuine amber should float. It may float at the surface, float mid-water, or float just below the surface depending on its exact SG within the 1.05–1.10 range. Pieces closer to SG 1.05 float higher; pieces closer to 1.10 float lower.

After testing: Remove the specimen and rinse thoroughly in fresh water. Dry with a soft cloth. Salt is not harmful to amber but residue can leave a white film if not rinsed off.

What Floats and What Sinks: Interpreting Results

Floats (SG below ~1.13): Genuine amber (1.05–1.10), copal (1.03–1.08), and very rare lightweight plastics. If the specimen floats, it is consistent with amber — but not confirmed as amber, because copal and rare plastics also float. Additional tests (UV, acetone, hot needle) are needed for positive identification.

Sinks (SG above ~1.13): Most plastics (1.2–1.5 typical), all glass (2.2–2.5), all mineral gemstones (2.5+), and pressed/reconstituted amber that has absorbed significant moisture. If the specimen sinks clearly and promptly, it is not amber. No additional testing is needed — the material fails the most basic physical property check.

Ambiguous (barely sinks or hovers): Some plastics have SG values close to saltwater density and may sink very slowly or hover mid-water. If the specimen does not float clearly, treat the result as inconclusive and rely on the other three authentication tests. The complete authentication guide explains the multi-test decision framework.

Limitations: What the Saltwater Test Cannot Tell You

The saltwater test is powerful as a negative screen — if it sinks, it is not amber. But it has real limitations as a positive confirmation.

Cannot distinguish amber from copal. Both are organic resins with similar SG values. Copal floats just like amber. This is the most important limitation because copal detection requires the acetone test specifically.

Cannot distinguish natural from pressed amber. Pressed amber (ambroid) has the same SG as natural amber because it is made from amber fragments. SG testing does not detect processing.

Can be fooled by composite materials. A plastic bead with an amber coating or a hollow plastic object might have an overall SG close to amber's range. These are rare in practice but theoretically possible.

Requires sufficient salt saturation. If the saltwater is not saturated enough (density below ~1.10), even genuine amber may sink — producing a false negative. Always dissolve maximum salt and confirm saturation by the presence of undissolved salt at the bottom.

Precision SG Measurement: Beyond the Kitchen

The saltwater float test is a pass/fail screen. For precise SG measurement, gemological methods exist that quantify the exact value.

Hydrostatic weighing: Weigh the specimen in air, then weigh it suspended in water. SG equals the air weight divided by the difference between air weight and water weight. This method requires a precision balance (0.01g resolution minimum) and a setup for suspending the specimen in water. It produces accurate SG values to two decimal places.

Heavy liquids: A series of liquids with known densities (diiodomethane at 3.32, bromoform at 2.89, etc.) can bracket a specimen's SG precisely. For amber, a diluted bromoform or sodium polytungstate solution calibrated to 1.05 and 1.10 would determine whether the specimen falls within amber's range. Heavy liquids are standard in gem labs but toxic — not recommended for home use.

For most buyers, the saltwater float test provides sufficient information. If the specimen floats, proceed with the other three tests. If it sinks, it is not amber. Precision SG measurement is for gemological laboratories and serious collectors who want exact documentation of their specimens' properties. The refractive index and optical properties guide covers the complementary RI measurement.

Combining SG With Other Tests for Complete Authentication

The saltwater float test is one of four tests in the standard blue amber authentication protocol. Each test targets different imitation materials, and together they provide comprehensive coverage.

Saltwater test (SG): Screens out most plastics and all glass and mineral imitations. Fast, non-destructive, requires no equipment. First test to perform because it eliminates the majority of fakes immediately.

UV test (365nm fluorescence): Confirms blue fluorescence — the defining property of blue amber. Screens out non-fluorescing materials and materials with wrong fluorescence colour. Requires a 365nm UV flashlight.

Acetone test: Detects copal (becomes tacky) and surface coatings (dissolve). Critical because copal passes both saltwater and UV tests. Apply acetone to a small inconspicuous area.

Hot needle test: Confirms organic origin (pine-resin scent) and screens out plastic (chemical smell) and glass (no smell). Destructive — leaves a tiny mark. Test last, on a hidden area.

A specimen that passes all four tests is genuine blue amber. A specimen that fails any test requires explanation. The fake blue amber guide provides the complete decision tree for interpreting mixed results.

Frequently Asked Questions

Does blue amber float in saltwater?

Yes. Blue amber has a specific gravity of 1.05–1.10, which is less than saturated saltwater (~1.13 g/cm³). Genuine amber floats in saltwater while sinking in fresh water. This is one of the simplest and most reliable authentication tests for amber.

How do I do the saltwater float test for amber?

Dissolve as much table salt as possible in warm water (approximately 7–8 tablespoons per 300ml). Stir until fully dissolved. Drop the specimen in. Genuine amber floats. Most plastics and all glass sink. Rinse the specimen in fresh water afterward to remove salt residue.

What sinks in saltwater that looks like amber?

Most plastic imitations (SG 1.2–1.5), glass (SG 2.2–2.5), and mineral gems all sink in saturated saltwater. Some very lightweight plastics may hover or float slowly, so combine the saltwater test with UV, acetone, and hot needle tests for complete authentication.

Does copal float in saltwater too?

Yes — copal has a similar specific gravity to amber (approximately 1.03–1.08) and will float in saltwater. The saltwater test cannot distinguish amber from copal. Use the acetone test (copal becomes tacky, amber does not) to detect copal specifically.

Can the saltwater test damage blue amber?

No. The saltwater float test is completely non-destructive. Salt water does not chemically affect amber. Simply rinse the specimen in fresh water after testing to remove any salt residue, and dry with a soft cloth.