What is a glaze in painting?

A glaze is a thin, transparent or semi-transparent layer of paint applied over a dry underlayer. Light passes through the glaze, hits the layer below, and reflects back through the glaze — creating a luminous, jewel-like depth that cannot be achieved with opaque paint.

How many glaze layers do Old Master paintings use?

Old Master oil paintings typically used 3 to 15 or more glaze layers, built over weeks or months. The dead colour (grisaille) underpainting was overlaid with successive transparent colour glazes. The final surface could be 10–20 thin layers deep.

Why does a white ground produce more luminosity?

A white ground reflects maximum light back through the glazes. Each photon passes through the glaze layers twice — once going in and once returning — doubling the colour-modifying effect. Dark grounds absorb light rather than reflecting it, producing rich but less luminous results.

What is the difference between a glaze and a scumble?

A glaze is a transparent dark colour applied over a lighter layer. A scumble is an opaque or semi-opaque light colour applied over a darker layer. Both build optical depth but through opposite mechanisms. This calculator handles both: low opacity values are glazes, higher values approximate scumbling.

How do I calculate glaze opacity?

Mix a small amount of paint into a clear medium and brush it across a strip of black and white card. The opacity is how much the underlying card shows through. Many pigments are naturally transparent (e.g. alizarin crimson, phthalo blue) while others are opaque (titanium white, cadmium yellow).

Glaze Layer Calculator — Cumulative Opacity & Depth

How We Calculate This

The calculator treats each transparent glaze as a filter that passes a fraction of the light, then stacks those filters (the Beer-Lambert multiplicative model). Light travels down through every layer, reflects off the ground, and returns through the layers again:

Formulas

Effective opacity per layer = set opacity × (1 − dilution / 100)
Transmittance per layer = 1 − (effective opacity / 100)
Total transmittance = (Transmittance per layer) ^{number of layers} × drying factor
Cumulative opacity = 1 − Total transmittance
Optical density = −ln(Total transmittance) — the standard layered-absorbance measure
Layers for full coverage = log(0.05) ÷ log(Transmittance per layer), i.e. the count needed to reach 95% cumulative opacity

Advanced options: the dilution ratio thins the paint with medium so each layer reads more transparent; the drying factor (0.5–1.0) trims transmittance to model the slight clouding of glazing onto a not-quite-cured layer — it can only reduce clarity, never add it. The refractive index feeds a separate qualitative depth band (a relative richness estimate, not a derived physical quantity).

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always verify quantities before purchasing materials.