1. Atmospheric Environment Type
Rural clean airPatina forms slowly and evenly; final color tends to be warm, medium-to-dark brown with less gray tone.
Urban / industrial atmosphere (SO₂, acid rain, dust)Accelerates patina maturation; color becomes darker, grayish-brown or dark coffee brown; more stable and deeper.
Coastal salt-spray environmentChlorides disrupt patina formation; color appears uneven, patchy red-brown mixed with dark spots; may stay bright for longer.
2. Humidity, Rainfall & Wet‑Dry Cycle Frequency
Frequent wet-dry cycles promote uniform, dense patina and faster darkening.
Long-term high humidity or poor ventilation leads to soft blackish rust and streaky color.
Heavy and frequent rain washes away surface impurities, resulting in more uniform color and less runoff.
Arid, dry climate slows oxidation; color darkens slowly and may remain lighter for years.
3. Sunlight & Ultraviolet (UV) Exposure
Full outdoor sunlight accelerates oxide conversion and makes color deepen steadily.
Shaded, low-light areas form patina slowly; color is dull, uneven, and darker in a non-uniform way.
UV radiation promotes the transformation from loose rust to stable goethite, which is the main reason for gradual darkening.
4. Surface Condition & Processing Method
Hot-rolled original surface oxidizes gradually; color changes naturally from orange-red to dark brown.
Sandblasted / ground surface starts rusting faster and colors more uniformly.
Rust-converted or pre-rusted surface skips the bright stage and directly enters a darker mature state.
Welds, cutting edges, and stamped areas have different composition and roughness, leading to local color differences.
5. Steel Plate Thickness & Surface Roughness
Thicker plates have a slightly slower surface reaction rate but more stable final color.
Rougher surfaces hold moisture and rust more easily, leading to darker and slightly uneven color.
Smoother surfaces form a finer, more uniform patina.
6. Pollution & Deposits
Dust, dirt, and industrial particles accumulate and cause local dark spots or uneven color.
Acid rain accelerates patina densification, making the overall tone darker and grayish.
Salt, chemical deposits damage the protective layer and cause patchy, unstable color.
7. Structural Design & Drainage
Good drainage and ventilation support normal patina development and even color.
Pockets, gaps, and lap joints trap water and dirt, causing dark streaks, black rust, and obvious color differences.
Contact with concrete, wood, or soil causes local discoloration and accelerated corrosion.
8. Time & Patina Maturity Stage
Early stage (0–3 months): bright yellow → orange-red.
Medium stage (3–18 months): deepens to reddish brown → coffee brown.
Long-term stable stage (1–5 years): matures to dark chocolate brown / grayish brown and no longer changes significantly.
9. Temperature
Moderate temperature (10–25°C) favors ideal patina formation and normal color darkening.
Extremely low temperature slows oxidation; color change is almost stagnant in winter.
High temperature (above 300°C) destroys the patina and forms loose red oxide, losing the natural weathering color.
