This publication throws new light on the remarkable quality of the iron castings made at Canada’s historic firs ironworks, Les Forges Saint-Maurice. A brief outline is provided of the history of that famous enterprise, located eight miles from Trois-Rivieres, Province of Quebec. It was founded in the days of New France, over two hundred and thirty years ago (1738). The blast furnace was finally closed down for good in the year 1883. A few rough stone foundations are all that remain today on that historic site. This new information on early cast iron in Canada is the outcome of an investigation, by the Mines Branch, of the exact nature of the iron in the Potash Kettle shown in Figure 1. This remarkable large casting is fully authenticated as a product of Les Forges Saint-Maurice, by the cast-in-foundry mark, F St M, clearly to be seen on the lip of the vessel. Castings, of any kind, bearing this trade mark are exceedingly rate. There are only a few such pieces, mostly stoves, in museums and with private collectors. This design of kettle is believed to be the largest casting made in Canada, before Confederation Year 1867, using iron smelted from native ore. This study at the Mines Branch Research Laboratories was undertaken as part of an investigation by the author into the use, by pioneer settlers in Canada, of large cast iron vessels in their making of potash alkali from hardwood ashes. The description of that process, given in Chapter II, contributes considerable new information on the history of the little known technology of that pioneer pursuit. Some historical perspective is provided in a brief review o f the role of modern potash from Saskatchewan mines as the ‘commercial successor’ of the potash made from wood-ashes in settlement days. The iron made at Saint-Maurice was smelted with charcoal from a very pure bog-iron ore found nearby. The Research Laboratory reports (Chapter III) show this iron has a composition very low in harmful impurities and favourably compares with historic Swedish charcoal irons, which were the world’s standard of excellence for several hundred years (Chapter IV). The investigation revealed that the iron in the potash kettle, now at Sutton, Quebec, has outstanding quality in its resistance to red-heat temperatures and corrosion. This is demonstrated in a detailed comparison with modern foundry practice in the making of chemical processing vessels (Chapter V). This publication is specifically designed to serve two groups of readers. The general text with illustrations is for that growing group of Canadians with a broad general interest in reading the story of pioneer times in this country. The annotated bibliography supplements the text, especially for that smaller group of readers in Canada and elsewhere whose interest is the detailed history of technology of pioneer pursuits. Up to now, that has been a neglected field in Canadian history. There is much enthusiasm, today, among prominent citizens of the thriving city of Trois-Rivieres, for more formal recognition of their cultural heritage in what has been described as ‘The Romantic Birthplace of Canadian Industry.’ Their suggested program takes the form of restorations on the site of Les Forges Saint-Maurice, along with a museum for historical articles and documents. For the past three summers, archaeological teams in The Quebec Provincial Authorities have been doing significant work on the site, which was acquired, a few years ago, by the Quebec Historical Monuments Commission. It is the hope of the author and the research scientists at the Mines Branch that this publication may assist in such a commendable project by contributing to a better understanding of the history of charcoal-iron technologies at Canada’s historic first ironworks, Les Vieilles Forges, at Saint-Maurice