1. Surface treatment before installation
Shot blasting / sanding: rougher surface → faster & more uniform color change
Oil, rust preventive, mill scale not removed: color becomes patchy, slow to react
Polished too smooth: rust layer forms unevenly, appears streaky
2. Processing and manufacturing factors
Cutting, bending, welding marks:Welded areas & bent zones have internal stress & oxide layers → darker, faster color change
Surface scratches:Scratched areas rust first, forming light/dark patches
Inconsistent material batch:Different batches of SPA‑H may have slight composition differences → slightly different final color
3. Installation conditions
Orientation toward sunlight:South‑facing / strong UV → darker & fasterShaded side → lighter, slower
Contact with other materials:Touching cement, stone, wood, soil → absorbs moisture → dark spots or discoloration
Ventilation condition:Poor ventilation → long‑term damp → loose orange rust, hard to darken evenly
4. Rainwater and water flow effects
Vertical signs: easy to have rust runoff streaks
Horizontal / recessed areas: water retention → light ring stains or dark patches
High‑altitude / strong wind: faster drying → more even patina
5. Human factors and later interference
Accidental touching, graffiti, cleaning with chemicals:Damages the forming rust layer → color inconsistency
Sprinkling by nearby irrigation systems:Frequent uneven wetting → patchy color
6. Service life and aging of the patina
Early stage: bright red → unstable
Mid-term: dark brown → gradually stable
Long-term: slight deepening or slight fading depending on UV & acid rain
If not protected, the surface may become powdery and look lighter over time
7. Pollution and dust attachment
Dust, oily fumes, metal particles attached to the surface
Forms local corrosion → color spots, unevenness
