Hydrostatic Weighing Using a Modern Single-Pan Electronic Balance

Learn how to use a modern single-pan electronic balance for hydrostatic weighing. Step-by-step guide to measure gemstone specific gravity with accuracy.

Hydrostatic weighing is one of the most reliable ways to measure the specific gravity of gemstones. With a modern single-pan electronic balance, the process is faster and more accurate than the old twin-pan balance.

You can even measure stones smaller than 3 carats with confidence.

What You Need

• A modern electronic carat balance
• A lightweight beaker filled to the top with distilled water
• A simple stand with a thin wire attachment
• A small wire cage or basket to hold the stone

The beaker can be as simple as the lid of an aerosol can or a 35 mm film canister. The wire cage should be light and positioned so it does not touch the sides of the beaker.

Step 1: Weigh in Air

Place your stone directly on the balance pan.
Record its weight in air.

Step 2: Set Up Water Beaker

Remove the stone.
Place the water-filled beaker on the stand under the balance pan.
Make sure the cage is fully submerged and not touching the container sides.
Zero the balance.

Step 3: Weigh in Water

Carefully lower the gemstone into the wire cage.
Ensure no water spills onto the balance pan.
Record the new weight reading.

Step 4: Calculate Specific Gravity

Use this formula:

• Weight in Air ÷ (Weight in Air – Weight in Water)

Example:
If your stone weighs 2.50 ct in air and 2.00 ct in water:

• Loss in water = 2.50 – 2.00 = 0.50
• SG = 2.50 ÷ 0.50 = 5.00

Why This Matters

• Helps you separate look-alike stones.
• Confirms identity and authenticity.
• Adds accuracy when testing smaller gems.

Have you ever compared SG readings of similar-looking stones?
You’ll be surprised how this simple test can reveal big differences.

Hydrostatic weighing with a single-pan electronic balance makes measuring gemstone specific gravity quick and accurate. You only need a simple stand, a beaker of distilled water, and a wire cage. Weigh the stone in air, then in water, and apply the formula. This method helps you identify and separate gemstones with confidence, even below 3 carats.