Add Colorant to Wet Glaze Calculator
Use a weighed glaze sample to estimate how much dry base is in a wet bucket, then find the dry additive weight for your chosen percentage. Choose a Brongniart estimate when the base density is known, or a dried sample when you can measure the residue directly.
Additive to weigh75
- Measured glaze specific gravity
- 1.45
- Estimated dry-solids percentage
- 51.72%
- Dry base glaze in the bucket
- 1,500
- Estimated water in the bucket
- 1,400
- Final dry-solids weight
- 1,575
- Additive share of final solids
- 4.76%
- Estimated wet batch weight after addition
- 2,975
All weights are grams; the calculated addition is dry material added to the existing wet glaze.
Use a thoroughly mixed, representative sample, then recheck specific gravity and application after mixing in the additive.
How to use this calculator
- Stir the glaze until the sample is representative, then record the bucket volume and the empty container weight.
- Fill the container exactly to its measured sample volume, weigh it, and enter the container-plus-glaze weight.
- Choose Brongniart estimate and enter the blend specific gravity, or choose dried sample and enter the residue weight without the container.
- Enter the additive percentage and whether it is an addition on top of the base or a share of final dry solids.
- Weigh the calculated dry additive, mix it in completely, and test a small sample before treating the full bucket as final.
Calculating colorant for an already-wet glaze
Glaze recipes are normally written by dry weight. A colorant listed as 5% is usually 5 g added to every 100 g of dry base glaze, not 5% of the wet slurry in the bucket. When the original dry batch weight is unknown, the first job is to estimate the dry base represented by the wet glaze you have.
Weigh a known volume of well-mixed glaze. If the empty container weighs T, the filled container weighs F, and the sample volume is v, net wet sample mass is w = F − T and measured specific gravity is G = w ÷ v. For total bucket volume V, estimated wet batch mass is M = G × V.
Two ways to estimate the dry base
With Brongniart's formula, enter p, the specific gravity of the blended dry materials. The dry base estimate is D = V × (G − 1) × p ÷ (p − 1). This treats the slurry as water plus one blended solid phase, so its usefulness depends on both the density value and the quality of the sample.
A dried sample avoids assuming that density. Dry the measured sample completely, weigh the residue d without its container, and use D = (d ÷ w) × M. This is generally the more direct measurement when the sample was representative and all water has been removed without losing material.
On top of the base versus final solids
For the usual recipe convention, a target r% is added on top of the base: A = D × r ÷ 100. Thus 5% means 5 g of additive with 100 g of dry base, for 105 g of total dry solids. Glazy describes colorants and opacifiers as additional ingredients and gives the same 100 g base plus 1 g additive pattern.
If a specification instead says the additive itself must be r% of final dry solids, use A = D × r ÷ (100 − r). A 5% final-solids target needs 5.263 g per 100 g base, because 5.263 g is 5% of the resulting 105.263 g total. The calculator also reports the final solids, water estimate, and post-addition wet weight so the percentage convention remains visible.
What moves the result and what it leaves out
Settling, foam, air bubbles, an inaccurate fill line, and an unrepresentative bucket-volume estimate can all move the answer. Brongniart's result also moves with the dry-material specific gravity; dried-sample results move with whether the residue was completely dried and retained. Neither method measures viscosity, thixotropy, application thickness, slurry-volume change, glaze chemistry, fired color, fit, durability, or leaching. Powder additions can alter suspension and rheology, so mix thoroughly, recheck the specific gravity, and test-fire before committing work.
Worked example
Suppose a 2,000 mL glaze bucket is sampled in a 100 mL cup. The empty cup weighs 50 g and the filled cup weighs 195 g, so net sample mass is 145 g and specific gravity is 145 ÷ 100 = 1.45. With a dry-material specific gravity of 2.5, the Brongniart estimate is 2,000 × (1.45 − 1) × 2.5 ÷ 1.5 = 1,500 g of dry base.
For a 5% colorant addition on top of that base, weigh 1,500 × 0.05 = 75 g. Final dry solids are 1,575 g, so the colorant is 4.76% of final solids and estimated wet batch weight after addition is 2,900 + 75 = 2,975 g. If the same 5% target means a share of final solids instead, weigh 1,500 × 5 ÷ 95 = 78.95 g.
Common questions
Is glaze colorant percentage based on wet or dry weight?
Colorant percentages in ceramic recipes are normally based on the dry base glaze weight. A 5% stain addition usually means 5 g of stain per 100 g of dry base, even if water was later added to make a dipping glaze. Confirm the convention when working from a supplier instruction or a technical test.
What is the difference between 5% on top and 5% of final solids?
Five percent on top means adding 5 g to 100 g of dry base, making 105 g of final solids; the additive then represents 4.76% of that final total. Five percent of final solids means the additive must be 5% after it is included, so it requires 5.263 g for each 100 g of base. Most glaze recipes use the on-top convention.
How do I measure glaze specific gravity with a cup and scale?
First weigh a clean, dry cup. Fill it to a known volume with thoroughly mixed glaze, weigh it again, subtract the cup weight, and divide net grams by milliliters. A 145 g glaze sample in a 100 mL cup has a specific gravity of 1.45.
Is Brongniart's formula accurate enough for Mason stains?
It can be useful for estimating the dry base in a mixed wet glaze when the blended dry-material specific gravity is realistic. It does not predict a stain's fired color or account for every ingredient's density, dissolved material, or slurry behavior. A dried sample gives a more direct solids estimate, and a small test firing remains necessary.
Why is a dried sample more accurate than an assumed material density?
A dried sample measures the dry residue in the actual glaze rather than inferring it from an average particle density. It still relies on a representative, completely dried sample with no lost solids. Use a small, accurately measured sample and mix the bucket well before taking it.
Can this calculator be used for oxides, opacifiers, and bentonite?
Yes, the mass calculation works for any dry additive expressed as a percentage of the base or final solids. The practical effect is different for each material: some change color, some opacity, and bentonite can strongly change suspension and viscosity. Check the material guidance and test a small batch first.