At the beginning of the century the Iser Mountains had also become an important hub for the Bohemian textile industry with the mills ranking among the largest in the Empire. Josef wanted to be involved in textiles: in 1858, he began to build a modern cotton mill on the main Giant Mountain road at Grünthal on the Iser River. The mill was fully operational in 1862 and continued to expand as business was good; 5,000 spindles of cotton were produced here annually. In 1868 the mill was rebuilt again and production doubled to 10,000 spindles per annum. Some of the equipment came from a mill in Polaun, which Josef Riedel had bought at auction in the previous year from none other than Ignaz Friedrich.