Production at Glen Lean is known to have begun around 1840, and continued into in the early years of the 20th century, although there is no precise date listed for the final closure of the mill.
The substantial ruins of the old village of Clachaig, and the mill workings, give an indication of the size of the venture. The village was built specifically to house the workers, and had cottages for the workers, a grand house for the manager, and various buildings devoted to production of the powder itself. The whole site was surrounded by a high wall for security. Explosions were a constant risk, and nothing made of steel or ferrous material was permitted on site. Tools were made of materials such as wood, brass, or copper, as were the worker's clogs.
Much of the site still remains in the form of substantial ruins, with some of the cottages having been restored