Pig iron had been exported from Virginia and Maryland since the 1720s, but little came from other colonies, nor did bar iron. The continuance of this was encouraged, as was the production and export of bar iron (which required a finery forge using a helve hammer not a trip hammer).
Conversely, the Act was designed to restrict the colonial manufacture of finished iron products and steel. Existing works could continue in operation, but no expansion would be possible in the output of:
- knives, scythes, sickles and other edged tools as a tilt hammer would be needed to produce thin iron, and a steel furnace to make steel.
- nails which were made from rod iron, from a slitting mill.
- Tinplate, which required a rolling mill. This was the raw material from which tinsmiths made a wide variety of goods from tinned sheet iron.
This was a continuation of a long term British policy, beginning with the Navigation Acts, which were designed to direct most American trade to England, and later Great Britain, and to encourage the manufacture of goods for export to the colonies in Britain.
The Iron Act, if enforced, would have severely limited the emerging iron manufacturing industry (as opposed to the production of cast or bar iron) in the colonies. However, as with other trade legislation, enforcement was poor because no one had any significant incentive to ensure compliance. Nevertheless, this was one of a number of measures restrictive on the trade of British Colonies in North America that were one of the causes of the American Revolution.
Part of the reason for lax enforcement may be due to the involvement of Colonial Officials in iron works. Virginia Governors Gooch and Spotswood were both deeply involved in iron manufacture. Gooch was a part owner of the Fredericksville Ironworks. Spotswood owned Tubal Ironworks (a blast furnace and probably finery forge) and the double air furnace at Massaponnax. Other prominent members of the Virginia aristocracy and House of Burgesses involved in the iron industry included John Tayloe II (Bristol Iron Works, near Fredericksburg; Neabsco Iron Works; and Occoquan Ironworks), Augustine Washington, George's father (Accoceek/Potomac Ironworks), and Benjamin Grimes (Grimes Recovery and a bloomery near Fredericksburg).