Patina Chemical Calculator — Solution Volumes

This calculator estimates the volume of patina solution and the weight of dry chemical needed from the surface area of your metal piece, the application method and the number of coats.

Solution volume

Volume per coat = Surface area × Application rate

• Brush: 0.02 ml/cm² (200 ml/m²) — a hot brushed coat covers ≈200 sq ft per US gallon (sculpturedepot.net), i.e. ≈18.6 m²/gallon ≈ 200 ml/m². An almost-dry wipe uses much less.
• Spray: 0.025 ml/cm² — spray is not more economical than brushing. Overspray bounces off the piece (transfer efficiency ≈65–80%), so a sprayed coat uses ~25% more solution than the same brushed coat.
• Immersion: 0.20 ml/cm² — a rough minimum only. A dip tank must hold enough to fully submerge the piece, so size the bath to the object, not to this per-area figure.

Chemical weight

Chemical = (Solution volume ÷ 1000) × Grams per litre × Concentration

Each preset uses a published recipe strength: liver of sulphur 5 g/L, ferric nitrate 50 g/L, cupric nitrate 100 g/L (Ganoksin 25 g/250 ml; Science Company), and the salt-based fuming methods 30–50 g/L salt — figures from the Science Company recipes and Hughes & Rowe, The Colouring, Bronzing and Patination of Metals. Patina solutions deteriorate within a day, so mix only what each session needs.

Safety: these are toxic, oxidising or irritant chemicals. Work outdoors or with forced extraction, wear chemical-resistant gloves and eye protection, use a respirator for nitrate and sulphide patinas, and capture run-off rather than letting it reach drains.