For me, rust provides the perfect organic appearance for an otherwise rather industrial material. 

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When steel first starts the oxidisation process it's orange, unstable and it will come off on anything it touches.  After a while, it gets darker in colour and becomes more stable.

 

Some more good old English drizzle and it will turn a rich burnt umber colour; this is the final stage and it will no longer come off.

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The steel has now formed its own protective coating and because I use heavier steel than garden centre plant supports it will last many, many years.