Stage 1 – Freshly manufactured Corten Steel. At this stage the dark oily residue coats the Corten Steel. Stage 2 – The oily residue is beginning to break down, as the Corten Steel begins to weather. Stage 3 & 4 – The “Run-Off” stage – This can take around 3 to 9 months depending on weather and positioning. Stage 5 & 6 – The final