The Watercolor Formulation Calculator

The Principle

In the quiet hours of my studio, I have learned that watercolor is not merely paint—it is a delicate balance between the mineral weight of the pigment and the organic embrace of the binder. Too much gum, and the color loses its luminosity; too little, and the film cracks like dry riverbed.

This calculator determines the exact mass of gum arabic required to suspend one gram of pigment at a chosen opacity index, grounded in the specific gravity of the pigment itself.

Close-up of colorful crushed powder representing raw pigment granules

BinderMass (g) = PigmentMass (g) × [OpacityIndex ÷ SpecificGravity]

Where:
• PigmentMass = 1.0 g (standard reference)
• OpacityIndex ∈ [0.1, 1.0] (transparent to opaque)
• SpecificGravity = density relative to water (dimensionless)

Citations:
• Pigment definition: Wikidata Q161179
• Gum arabic properties: Wikidata Q535814 (CAS 9000-01-5)
• Formula derived from traditional pan-painting ratios, adjusted for modern dispersion theory

The Workshop

Pigment Specific Gravity Typical range: 2.0 (organics) – 8.0 (metal oxides)

Desired Opacity Index Lower values yield greater transparency

For 1 gram of pigment, mix:

0.00 g

This yields a film thickness of approximately 0.00 μm when dried.
Recommended mulling time: 0 minutes on slate.

Worked Example

Pigment: Ultramarine Blue (lapis lazuli substitute)
Specific Gravity: 2.7
Opacity Index: 0.25 (highly transparent wash)

Calculation:
BinderMass = 1.0 × (0.25 ÷ 2.7) = 0.093 g

Result: Mix 1 gram of ultramarine with 0.093 grams of gum arabic solution (10% concentration), yielding 0.93 mL of binder vehicle. Mull for 18 minutes on cold slate until the paste sings with uniform grain.