It's the thickness of the gauge and the balance of the handle that determines its suitability, not its country of origin. The heavier the gauge, the better the heat distribution is. Gauge is simply the thickness of the metal and for copper should be one-eighth of an inch for optimum performance. A too thin layer of copper, such as is found coating the bottom of some stainless steel cookware, will not distribute heat as evenly as a solid copper pot since it hasn't the heft to hold and carry the heat sufficiently . Lined and Unlined What copper is lined with is not the least important consideration.
Copper is slightly acidic and reacts with certain foods and therefore usually is lined.
It is debatable whether the theory holds that egg whites beat to a significantly higher volume when whisked in a copper bowl. Dr. I. Herbert Scheinberg, professor at Albert Einstein College of Medicine in New York, thinks there is very little truth in it. The natural acidity in unlined copper causes egg whites to stabilize better. The author conducted a test to compare egg whites beaten in unlined copper to whites beaten in stainless steel. When two whites beaten in an unlined copper bowl were compared to the two beaten in a stainless steel bowl, the whites in the copper yielded one cup plus two heaping tablespoons.