Glass Color Mixing Calculator
Calculate glass color mixing ratios for frits and rods to achieve target hues.
Returns blends by weight based on additive and subtractive glass color mixing.
Glass color mixing follows subtractive color theory similar to paint mixing, but with important differences caused by the chemistry of metal oxides at high temperatures. Glass colors come from metal oxide colorants dissolved in the glass matrix, and the final color depends on the type of oxide, its concentration, and whether the atmosphere is oxidizing or reducing.
Primary Glass Colorants
| Metal Oxide | Color (Oxidation) | Color (Reduction) | Typical % by Weight |
|---|---|---|---|
| Cobalt oxide (CoO) | Deep blue | Deep blue | 0.1–0.5% |
| Copper oxide (CuO) | Turquoise/green | Red (copper ruby) | 1–3% |
| Iron oxide (Fe₂O₃) | Amber/brown | Green/blue-green | 1–5% |
| Manganese dioxide (MnO₂) | Purple/amethyst | Colorless | 1–5% |
| Chromium oxide (Cr₂O₃) | Green | Green | 0.1–1% |
| Gold chloride (AuCl₃) | Ruby/cranberry | Ruby/cranberry | 0.01–0.05% |
| Tin oxide (SnO₂) | White (opacifier) | White | 3–8% |
| Cadmium sulfide (CdS) | Yellow | Yellow | 1–5% |
| Selenium (Se) | Red/orange | Red/orange | 0.1–1% |
Color Mixing Formula (by weight)
When mixing two colored frits A and B:
Final Color Weight = Weight_A + Weight_B Ratio A = Weight_A / (Weight_A + Weight_B) × 100% Ratio B = Weight_B / (Weight_A + Weight_B) × 100%
For three-color mixes: Ratio A = Weight_A / (Weight_A + Weight_B + Weight_C) × 100%
Opacity Adjustment
Transparent glass can be made opaque by adding an opacifier (tin oxide or bone ash):
- Light opal: 3–4% tin oxide
- Full opaque: 6–8% tin oxide
- The opacifier weight is ADDED to the batch, not substituted
Common Color Recipes (Soda-Lime, COE 96)
| Target Color | Primary Frit | Secondary Frit | Ratio |
|---|---|---|---|
| Teal | Turquoise | Emerald green | 70:30 |
| Lavender | Clear | Purple | 80:20 |
| Coral | Orange | Pink | 60:40 |
| Forest green | Emerald | Black | 85:15 |
| Sky blue | Light blue | Clear | 50:50 |
| Olive | Amber | Green | 55:45 |
The calculator handles two colours. For a three-way blend such as peach (clear 60, orange 20, pink 20), mix two of them first, weigh the result, and treat that as one component of a second pass.
Worked Example: Making 100g of Teal
Primary: 70g Turquoise frit. Secondary: 30g Emerald Green frit. Mix thoroughly before applying. Too green, add turquoise. Too blue, add green.
For an opal teal, add 3g of tin oxide for a light opal or 7g for full opacity, giving a 103g or 107g batch. The opacifier is added to the batch, never substituted for part of it, so your colour ratio stays 70:30 either way.
Important Compatibility Warning
NEVER mix frits with different COE values. A COE 90 frit with a COE 96 frit will crack, and it will do it days or weeks later rather than in the kiln. Verify compatibility before mixing.
Even inside one COE family, test a small sample first. Some colorants fight: copper and sulfur together give a muddy brown rather than either expected colour, and silver-bearing glasses can bleach a neighbouring colour at the boundary.
Colorant safety
Several of the oxides in the table are genuinely toxic, not merely irritant. Cadmium sulfide and selenium are the ones to respect, and lead-bearing glasses are still sold. Powder frit is the hazardous form, because that is when it becomes airborne.
Work under extraction or in a fitted dust mask, wipe surfaces down wet rather than sweeping, keep food and drink out of the studio, and wash your hands before you leave it. None of this is onerous, and the exposure that matters is cumulative rather than dramatic.
Striking Colors
Some glass colors (especially reds, oranges, and some yellows) require striking, a reheat to a specific temperature after the first cooling. Gold ruby glass appears clear or pale pink until struck at 500–550°C, when the colloidal gold particles aggregate and produce the deep ruby color.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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