In 1760, he and his partner David Caldwell purchased land from Huber along Hammer Creek, and built Speedwell Forge.

Arriving penniless, his beautiful penmanship soon earned him a clerk position for the Reading Prothonotary.

After two years, he was hired by Peter Grubb Jr. as a clerk at Hopewell Forge, in Lancaster County.

Because of its distance from town, a forge had to be self-sustaining, employing farmers, lumberjacks, blacksmiths, horses, livestock, etc.

With the help of his father-in-law, Coleman leased Salford Forge, and began building his iron empire.

After selling Speedwell, James Old purchased an interest in Hopewell Furnace in Berks County, Pennsylvania.

Coleman reinvested his profits, buying many forges and furnaces, even the Cornwall iron mine.

The Speedwell property remained in the Coleman family, and they began breeding standardbred horses for sulky racing.

In 1942, Margaret Coleman Buckingham sold the Speedwell property, and surrounding 1,000 acres (4.0 km2), to Gerald and Kathryn Darlington.

In the 1960s, Pennsylvania state purchased about 500 acres (2.0 km2) along Hammer Creek and dammed it, creating Speedwell Forge Lake.

In 2006, the property, which included a summer kitchen and paymaster's office, was listed on the National Register of Historic Places.