## Architectural Metals Overview
| Material | Typical Life | Maintenance | Appearance Change |
|----------|-------------|------------|-------------------|
| 316 Stainless | 80-100+ years | Minimal | Retains brightness |
| Aluminum (anodized) | 40-60 years | Low | Slight dulling |
| Copper | 100+ years | None | Green patina (20-30 yr) |
| Weathering Steel | 80-100 years | None | Uniform brown oxide |
## Stainless Steel
**316**: Required for coastal, industrial, or polluted environments. The Chrysler Building's 304 cladding (installed 1930) remains excellent after nearly 100 years.
**304**: Acceptable for inland, low-pollution environments. Not recommended within 1 km of coastline.
Tea-staining (brown discoloration from surface contamination) is the most common defect. Prevention: specify 316 in marine environments and clean with nitric acid passivation after installation.
## Aluminum
**6063-T5**: Standard curtain wall extrusion alloy. Good surface finish and anodizing response. Clear or color anodized finishes per AAMA 611.
**PVDF coatings (Kynar 500)**: Maintain color for 30-40 years. AAMA 2605 specification.
## Copper
Develops green patina (copper carbonate) over 20-30 years. Pre-patinated copper available for immediate green appearance. The Statue of Liberty's C11000 copper skin (1886) demonstrates 100+ year life.
## Weathering Steel (Cor-Ten)
ASTM A588 forms a stable rust patina over 2-5 years. NOT suitable for continuously wet conditions, crevice-prone joints, or coastal environments.
## Life-Cycle Cost
Maintenance-free materials (stainless, copper) often cost less over 50-100 year building life than coated materials requiring periodic refinishing.
Choosing Alloys for Architectural Applications
Architectural metals must maintain appearance over decades while meeting structural and budget requirements. The choice between stainless steel, aluminum, copper, and weathering steel defines a building's aesthetic and maintenance trajectory.
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