Anodizing is an electrochemical oxidation process. The metal (titanium or niobium) is used as the anode (positive electrode) and placed in an electrolyte solution. When direct current is applied, a dense, transparent oxide film is grown in-situ on the metal surface
Anode: Titanium or niobium (oxidized to form oxide film)
Cathode: Stainless steel, titanium or graphite (only hydrogen evolution occurs, no film formation)
Electrolyte: Weak acid or neutral salt solutions (e.g., dilute sulfuric acid, phosphoric acid, oxalic acid, ammonium sulfate), which do not corrode the metal substrate
Color mechanism: Thin film interference (same as soap bubbles/oil films), no dye is involved; color varies with oxide film thickness.
Oxide titanium film is TiO₂ , it is Dense, non-porous, transparent barrier layer, Thickness: 10–200 nm, increases linearly with voltage: Film thickness ≈ 1.6–2.0 nm/. Oxide niobium is Nb₂O₅, and is also dense, transparent, with higher dielectric constant than TiO₂, Thickness: Increases with voltage, thicker than titanium oxide film at the same voltage
Anodizing colouring technique is used in both our niobium and titanium pieces by Xin in her home studio in Loughborough , these colours are strong, durable, permanent with long lasting wearability.
