Why did chromium salts replace many earlier mordants around 1850?

Around 1850, chromium salts began to replace many earlier mordants—such as those derived from alum, iron, copper, and tin—because they were found to provide superior dye retention on fabrics.1

By reacting with dyes to form insoluble compounds, mordants allow color to be held firmly to fibers that otherwise would not accept them directly, such as cotton. While ancient mordants were essential for varying the colors produced by a single dye, the introduction of chromium salts offered a more effective alternative for the industry. Today, chromium mordants remain widely utilized, particularly for wool, as well as for silk and nylon.1