Site photo of weathering steel planting pool

Quick answer：

Weathering steel, also known as atmospheric corrosion-resistant steel, is a type of steel that forms a stable rust layer on its surface when exposed to the atmosphere. This layer protects the steel from further corrosion. Weathering steel is often used in outdoor structures, such as bridges, buildings, and landscaping elements, including planting pools. The provided subject refers to a photograph showcasing a planting pool constructed with weathering steel.