How to get good rust!
I enjoyed the Corten fire build in Issue No. 76 and noted that Jude Woodside was hoping for a uniform rust covering on the fire. I have been using citric acid granules for this, which I buy from the Bin Inn shop, for around $10 per kilogram. All my new steel arrives with mill scale on it and this is not something you would weld to so I soak it in a solution of citric acid in an old plastic drum, which I cut in half lengthwise, or for small pieces just use a plastic bucket. The likes of 25x3mm or 6mm round I leave in overnight and wash off with water and a poly pad. The metal comes up a silver colour and will not rust up when building your project or when kept inside. Leave it outside and an even coating of rust will arrive.
The citric acid is great for any steel objects, but not good on cast iron.
Keith Beale, Gore, avid Shed reader