Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hi Ron

Get hold of some Citric Acid crystals it's quite safe to use it is used for home brewing and cooking. Dissolve as much crystals as the amount of water you use will take then pickle the boiler in it for a couple of hours then rinse with clean water the copper comes out a nice pink colour. The pickle can be kept for further use in an old ice cream tub with a lid. The  Citric Acid can be bought from home brew shops or online I bought my last lot from Amazon it is not expensive a 1kg bag will last forever at only a few £.
Paul.