1. Pre-Treatment: Foundation for Uniform Patina
Mechanical Cleaning
Sandblasting: The most common method for industrial parts. Use fine aluminum oxide grit (80–120 mesh) at low pressure (0.2–0.4 MPa) to remove mill scale, rust, and oil residues. Target surface roughness: Ra 3–5 μm-this texture provides nucleation sites for uniform patina growth without creating deep scratches that trap moisture.
Wire Brushing: Suitable for small parts or touch-ups. Use a soft stainless steel wire brush to avoid surface damage; ideal for removing light surface contaminants after fabrication.
Chemical Degreasing
Wipe parts with isopropyl alcohol or a neutral degreasing agent to remove oils from cutting, bending, or handling. Oil residues block oxidation, leading to patchy, light-colored spots on the final patina.
Rinse thoroughly with clean water and air-dry completely-residual water spots cause localized corrosion.
2. Active Patina Acceleration: Shorten Natural Weathering Time
Standard Accelerator Formulation (Water-Based, Low-Toxicity)
Key components: 2–5% ferric chloride, 1–3% copper sulfate, trace organic acid (to adjust pH to 3–4). This mimics natural environmental corrosion (salt, moisture, CO₂) and promotes the formation of a dense, copper-rich patina layer (主要成分是 FeOOH 和 Cu₂O).
Application & Curing Process
Apply the accelerator evenly via spraying or brushing-ensure full coverage of edges, welds, and recessed areas (these are high-risk zones for uneven patina).
Cure parts in a controlled environment: temperature 20–30°C, relative humidity 70–90%. Rotate parts every 12 hours to ensure all surfaces are exposed to moisture and oxygen.
After 3–5 days, rinse parts with clean water to remove residual accelerator ions-this prevents over-corrosion and locks in the uniform reddish-brown patina.
3. Passivation & Sealing: Preserve Patina Longevity
Breathable Sealant Coating (Recommended)
Use a fluorocarbon-based transparent breathable sealant. It penetrates the patina's porous structure to block salt and moisture penetration, while allowing the steel to "breathe" (prevents blistering or peeling). This extends patina service life by 2–3 years without hiding the steel's rustic texture.
Application method: Spray a thin, uniform layer (wet film thickness 10–15 μm) after the accelerated patina is fully dry.
Passivation for High-Corrosion Environments
For parts exposed to heavy salt spray, apply a chromate-free passivation agent after rinsing. This forms a thin protective film on the patina surface, further inhibiting stress corrosion cracking (SCC).
4. Post-Treatment Maintenance: Sustain Patina Uniformity
Initial Period (First 1–3 Months Post-Installation): Rinse parts monthly with low-pressure water to remove dust, bird droppings, or mineral deposits. Avoid acidic/alkaline cleaners that erode the patina.
Long-Term Care: For sealed parts, reapply the breathable sealant every 2–3 years. For unsealed parts, minor scratches will self-heal over time as the steel reacts with the environment.
