ADVERTISEMENT
Iron Pillar (400 AD)
In the Middle Ages, some artisans knew how to coat materials with a thin layer of metal like gold and silver, and in some ways, their metal coating techniques were better than modern ones. One of the amazing objects with such a metallic coating is the Iron Pillar in Delhi. This is a seven-meter-tall column, which has remained free of corrosion for one and a half thousand years. The secret is that the composition of the material from which the column is made contains a large amount of phosphorus; it also saves metal from rust.
