We have all seen them – a batterie of coppers in the kitchen of a stately home; a gleaming row of professional kit with a glorious heritage kick.
I have found a very thorough and well written article on the subject by Four & Twenty http://vintagecoppercookware.com/about-antique-copper-cookware/
It sets out some very clear advice for newbies: ‘There are, however, a few fundamental bits of knowledge that may be helpful to a fledgling collector of copper. For example, you will often see antique copper-ware described as having dovetailed seams. These seams go up one side of the piece and circle around the bottom. When making a saucepan or stockpot, the copper-smith would first cut a rectangle of copper to form the sides of the pot. He would then hammer the edges of the two short sides until they were about half as thick as the rest of the piece. Next, he cut slits on one side (or, in some cases, on both sides) and folded up every other tab. The two sides were then fit together, the tabs flattened and hammered, and the seam brazed for a perfect seal.
After the sides of a pot were joined, creating a cylinder, the floor of the pot was fashioned and attached.
The smith would start by turning in the lower edge of his cylinder, making a lip about an inch wide. He did this by hammering it over a form. This was the hardest part, the part in which he was most likely to ruin his pot by breaking the copper at the point where it turned. Once the lower edge was successfully turned in, the next step was to cut a circle of copper to make the floor (sometimes you can still see the mark left by the point of the compass the smith set in the centre to draw a perfect circle of exactly the right size). He would then dovetail the edges of the circle and/or the turned-in lip, and join them as he had the side seam. Dovetailing requires extraordinary skill acquired through long, dedicated practice. It is so difficult that you can generally assume a dovetailed pot really is an antique. It would hardly be worth the effort to fake it today.’