the sculpture was made from the same weathering steel (also known as cor-ten) as the angel of the north sculpture. this slowly develops a tightly adhering oxide layer as it is exposed to the elements. this layer prevents further corrosion by reducing its permeability to water. as part of the design, the spikes moved slightly in the wind in order to withstand gusts over . at the time of construction a time capsule was placed in one of the spikes of the sculpture. it contained children's poems and paintings, due to be opened around 2300. the location of the time capsule after being taken apart is currently unknown.