Glaze Specific Gravity Adjustment Calculator
Enter a weighed glaze batch, or use two hydrometer readings and a weighed water addition when the bucket cannot be lifted. The calculator estimates solids, water, the signed water adjustment, and a dry-glaze alternative when raising specific gravity.
Water adjustment (g)370.37
- Estimated dry glaze solids (g)
- 2,676.77
- Estimated water in batch (g)
- 2,323.23
- Adjustment instruction
- Add 370.4 g of water in stages, mix completely, then remeasure.
- Target wet batch weight (g)
- 5,370.37
- Target batch volume (mL)
- 3,703.7
Assumes water density is 1 g/mL and the glaze is fully mixed before each reading.
Removing mixed slurry removes solids with the water and does not materially raise specific gravity.
How to use this calculator
- Choose whether you know the wet batch weight or need the two-reading test.
- Enter the starting specific gravity and, for the two-reading test, the weighed water addition and second reading.
- Enter the target specific gravity and the dry-material specific gravity for the glaze powder.
- Use the signed water adjustment, then mix thoroughly and remeasure before making a final correction.
How the glaze adjustment is calculated
Specific gravity is the mass of a glaze slurry divided by the mass of the same volume of water. For studio glaze work, water is treated as 1 g/mL, so a 1.45 glaze weighs 1.45 g per mL. This calculator uses that mass balance to estimate how much water must be added or removed to reach a target reading.
Let G be the current specific gravity, T the target, M the current wet mass, P the dry-material specific gravity, S the dry-solids mass, W the water mass, and V the current volume.
V = M / G
S = M x P x (G - 1) / [G x (P - 1)]
W = M - S
The signed water adjustment is:
y = M x (G - T) / [G x (T - 1)]
If y is positive, add that many grams of water. If it is negative, remove that many grams of water by controlled evaporation or by decanting clear supernatant after the glaze has settled. Removing mixed glaze is not the same thing, because it removes solids in the same proportion as water.
When the bucket cannot be weighed
The two-reading mode estimates the starting wet mass from a known water addition. Let G0 be the first reading, G1 the reading after adding A grams of water, and M0 the original wet mass. The inferred mass is:
M0 = A x G0 x (G1 - 1) / (G0 - G1)
The calculator then uses M = M0 + A and G = G1 for the adjustment. This method depends strongly on the difference between the two readings, so a small test-water addition can make the inferred weight noisy.
Raising specific gravity
To raise specific gravity with water removal, the tool returns a negative water adjustment. It also gives a dry-glaze alternative when the target is above the current reading. That estimate assumes the added powder has the same composition and particle specific gravity as the suspended glaze solids:
x = [T x (S / P + W) - (S + W)] / (1 - T / P)
What this calculator leaves out
Specific gravity is not viscosity. Two glazes at the same reading can dip differently because of clay content, flocculation, deflocculation, soluble salts, particle size, settling, temperature, entrained air, and mixing history. The solids estimate also depends on the dry-material specific gravity you enter; 2.65 is a useful general estimate, not a measured value for every glaze.
Worked example
Suppose a weighed glaze batch is 5,000 g at a specific gravity of 1.50, and the target is 1.45. With a dry-material specific gravity of 2.65, the estimated dry solids are 2,676.77 g and the estimated water in the batch is 2,323.23 g.
The water adjustment is 5,000 x (1.50 - 1.45) / [1.50 x (1.45 - 1)] = 370.37, so add about 370 g of water in stages. The target wet batch weight is 5,370.37 g, and the target batch volume is 3,703.70 mL.
Common questions
How do I calculate glaze specific gravity with a scale and graduated cylinder?
Tare the empty graduated cylinder, fill it to a known volume with well-mixed glaze, and weigh the glaze. Divide the glaze weight in grams by the volume in milliliters. For example, 145 g in a 100 mL cylinder has a specific gravity of 1.45.
How much water should I add to lower glaze specific gravity?
Use the signed water adjustment from the calculator. A positive value is grams of water to add, and because water is close to 1 g/mL, the same number is also milliliters. Add most of it, mix, and remeasure before adding the last part.
Can I calculate a bucket's glaze weight without lifting the bucket?
Yes, if you can add a known weight of water and take accurate specific-gravity readings before and after. The two-reading mode uses the drop in specific gravity to infer the original wet batch mass. The readings must be far enough apart to avoid a noisy result.
How can I raise specific gravity without waiting for water to evaporate?
If you have matching dry glaze powder, the calculator estimates how much powder to add. This works best when the dry mix is the same recipe and is screened or slaked well enough to disperse completely. Otherwise, controlled evaporation or decanting clear water after settling is safer.
What dry-material specific gravity should I use for a pottery glaze?
A value around 2.65 is a practical estimate for many mineral ceramic materials. It is not universal, because frits, stains, opacifiers, and clay-heavy recipes can differ. If you have a measured particle specific gravity for the dry recipe, use that instead.
Why can two glazes with the same specific gravity behave differently?
Specific gravity describes density, not flow. Clay percentage, soluble salts, particle size, flocculation, deflocculation, and settling can make one glaze feel thick and another feel watery at the same reading. Always pair the number with an application test.