Glass Color Mixing Calculator
Calculate color mixing ratios for glass frits, rods, and powders to achieve target colors in hot glass work.
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 |
| Peach | Clear | Orange + Pink | 60:20:20 |
| Olive | Amber | Green | 55:45 |
Worked Example — Making 100g of Teal
Primary: 70g Turquoise frit. Secondary: 30g Emerald Green frit. Mix thoroughly before applying. If the result is too green, increase turquoise. If too blue, increase green.
For an opal teal, add 5g tin oxide (5% of 100g batch) for a total of 105g batch weight.
Important Compatibility Warning
NEVER mix frits with different COE values. A COE 90 frit mixed with COE 96 frit will cause stress fractures. Always verify COE compatibility before mixing. Even within the same COE family, test small samples first — some colorants interact unpredictably (e.g., copper + sulfur produces muddy brown instead of the expected colors).
Striking Colors
Some glass colors (especially reds, oranges, and some yellows) require “striking” — reheating to a specific temperature after initial 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.