Glaze Specific Gravity & Brongniart Calculator (Dry Material, Water to Add)

How it works

SG = sample weight ÷ sample volume · Brongniart: dry material D = (W − V) × ρ ÷ (ρ − 1), water = W − D · water needed for target SG_t: w = D × (1 − SG_t/ρ) ÷ (SG_t − 1); add or remove (w − current water) scaled to the batch

Specific gravity (weight of a known volume relative to water) is the one number that makes glaze application repeatable from bucket to bucket and week to week. Brongniart's formula separates that weight into dry material and water using the average density of the dry powder (≈ 2.6 for most glazes), which also tells you how much recipe you actually have in a bucket. Because water is the only thing that evaporates, adjusting SG is a matter of adding a measured amount of water or letting the glaze settle and decanting some off — this calculator turns your 100 mL test into that amount for the whole batch.

Worked example

A 100 mL sample of dipping glaze weighs 145 g: SG 1.450. With a dry-material SG of 2.6, Brongniart says it holds about 73.1 g of dry glaze (50.4% by weight) and 71.9 g of water. To bring a 4 L bucket down to a thinner SG of 1.40, each 100 mL needs 12.5 mL more water — about 500 mL for the bucket — after which the batch is about 4.5 L.

Frequently asked questions