Collusion developed at the biannual auctions of the East India Company from about 1779. This auction ring depressed the prices obtained at auction and so the trade became unprofitable. The import duty on tea was reduced from 119% to 12.5% in 1784. This increased the demand for tea and so it became the preferred cargo. In 1791, the Court of Directors ordered that, henceforth, china was only to be carried as ballast on their vessels. This reduced the import trade considerably and so, in 1795, the chinaman Miles Mason of Fenchurch Street, asked whether the company would carry private shipments of china for a carriage fee. They declined and Mason went on to develop a business in Liverpool and then Staffordshire. Mason wanted to develop a method of making replacement pieces for existing sets of china. His experiments led to the development of a type of pottery which, like Chinese porcelain, was strong and so resisted chipping. This was ironstone china which developed into a substantial business under his son, Charles, who patented the process. Many other potteries in England copied this style and large quantities were exported to other countries such as France and the United States. The original trade in imports from China ceased in 1798 as the East India Company stopped making bulk sales.