Baking in the 18th Century was performed in various types of ovens.
The Bread Ovens of Quebec
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The best book on building traditional clay ovens that reproduce the sort of oven in this period quote.

"The lowest part of the community are often debarred from the benefit of an oven from the expense of erecting one with brick and lime. The following method of making ovens, universally practised by every farmer in Canada, is worthy of imitation and adoption, as the poorest person may make one at little or no expence, save a tritling portion of pains and labour.

At a convenient distance from the house make a platform, of about six or seven feet square, of earth, stone, or wood ; raise it about three feet from the ground; procure a quantity of clay, and one third of sand ; beat and mix it well with water to the consistence fit
for making bricks. With this clay cover the top of the square about six or seven inches thick, and make it perfectly smooth and level. Provide a number, of
laths, twigs, or small branches of trees, which will easily bend into an oval shape. On the moist clay, mark out the size of the oven; then bend the twigs, or other materials, into the shape and size of the oven, leaving at one end, a
vacancy for the door of the oven, in proportion to the size, sticking the ends of them into the clay. When finished, it will appear like a basket, turned
upside down. The next step is to plaster it over with clay, about an inch at a time, letting it dry a little at each time of plastering, till the thickness of eight or nine inches have been added. Then fill the oven with wood
or coals, and set it on fire; and where any cracks appear in the arch, work in some clay, and plaster it over. The fire must be continued till the whole is burnt to the state of a brick. An oven made in this manner, if properly covered from rain, will last a long time."

The seaman's guide : shewing how to live comfortably at sea : containing, among other particulars, complete directions for baking bread, either with yeast or leaven, in all situations : recommended also to public bakers, as well as to private housekeepers by John Cochrane, 1797

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Articles to come at a later date:

Dutch Ovens and Bake Kettles
Thoughts on using these tools in reenacting


Ovens at Historic Sites

The oven at Fort Michilimackinac