Indigo

Indigo is a beautifully symmetric molecule widely used as a dye. It has a very rigid and planar structure, making indigo highly insoluble. Because of this property, indigo only weakly dyes the surface of yarn. This "incomplete" dying enables denim to fade relatively quickly, resulting in an effect such as stone washing. It wasn't easy to process indigo due to its insoluble nature. Before the direct applications of indigo were developed, stale urine was used to chemically transform indigo into a soluble form. Despite those challenges, people loved indigo and were passionate about inventing technologies to leverage this material, allowing us to enjoy indigo products nowadays.