Indigo is one of the oldest dyes in the world, and for the Romans it came from one place: India. They called it indicum, “from India”, and the name stuck.
It was also one of the first things people learned to test. Two thousand years ago, Pliny the Elder wrote that real indigo, thrown on live coals, gives off a purple flame.
We test too. Every batch is checked for purity and identity, and its certificate is on the product page before it ships. Orders paid by 3 pm are packed and sealed the same day.
The seal on your box is our name in that colour, so you can see nobody opened it.
Pliny the Elder, Natural History, book 35. In Philemon Holland's 1601 translation: “cast the right indigo upon live coals it yieldeth a flame of the most excellent purple.”