A simple hydrostatic weighing method using Archimedes' principle

Density, also called specific gravity (SG) in gemology, is a useful physical property that can help evaluate or identify gemstone materials. A simple approximate density test can be performed at home with a digital scale, a container of water, and a thin thread.

What You Need

·       A digital scale that measures to at least 0.1 g. (A 0.01 g scale is preferable for greater accuracy; however, many 0.01 g scales have a limited weighing capacity. In this demonstration, my 0.01 g scale has a maximum capacity of 300 g, which is not sufficient for the water-container setup, so I used a larger scale with 0.1 g precision instead).

·       A container large enough to completely submerge the item

·       Clean water

·       A very thin thread or string

The item should be clean and dry before testing.

Step 1 - Measure the Dry Weight

Place the bangle directly on the scale and record its weight. In this example, the dry weight is 74.2 g. This is the mass of the bangle measured in air.

Figure 2. Measure the dry weight of the bangle: 74.2 g.

Step 2 - Prepare the Water

Place a container filled with enough water to completely submerge the bangle on the scale. Press the TARE/Zero button so the display reads 0.0 g. The container and water are now excluded from the measurement.

Figure 3. Place the water container on the scale and tare it to 0.0 g.

Step 3 - Suspend the Bangle in Water

Tie the bangle with a thin thread and carefully lower it completely into the water. It should be fully submerged and suspended freely, without touching the bottom or sides of the container. Remove any visible air bubbles attached to the bangle.

In this example, the scale reads 24.6 g. Because the water container was tared before immersion, this reading corresponds approximately to the mass of the displaced water. Under ordinary test conditions, 24.6 g of water corresponds approximately to 24.6 cm³ of volume.

Figure 4. Suspend the bangle completely in water without touching the container. Reading: 24.6 g.

Step 4 - Calculate the Density

Use the following formula:

Density = Weight in air ÷ Weight of displaced water

74.2 ÷ 24.6 = 3.016

Measured density ≈ 3.02 g/cm³

Example Result

Dry weight: 74.2 g
Displaced-water reading: 24.6 g
Calculated density: 3.02 g/cm³
Conclusion: The home density measurement is approximately 3.02 g/cm³, a value consistent with nephrite/Hetian jade.

Figure 1. Bangle and its identification certificate.

What Does a Density of 3.02 Mean?

The certificate visible in the photographs identifies the bangle as nephrite. A measured density of approximately 3.02 g/cm³ is consistent with the general density range expected for nephrite, commonly around 2.9-3.1 g/cm³ depending on mineral composition and natural variation.

Note: Density testing alone cannot prove that an item is nephrite. Professional gemological testing is recommended for definitive identification.

Tips for a More Accurate Test

·       Use a scale with at least 0.1 g precision; greater precision is even better.

·       Use the thinnest practical thread so the thread displaces as little water as possible.

·       Make sure the bangle is completely submerged.

·       Do not allow the bangle to touch the container.

·       Remove air bubbles from the bangle and thread.

·       Repeat the measurement several times. Similar repeated results increase confidence in the estimate.

Important: This is an educational home test. The scientifically appropriate wording is that the measured density is 'consistent with nephrite,' not that density alone proves the material's identity.