Yes, a copper bowl reduces the time and energy needed to whip egg whites. (The precise reason this phenomenon occurs is still being debated by scientists). Though this advantage is a welcome relief when you are using the arm-tiring, old-fashioned whisk method, it is of slight value with a manual or electric mixer. These efficient modern contraptions do their whipping chores almost as well in a stainless steel bowl.
A copper bowl also helps stabilize the beaten egg whites. If you are using a non-copper bowl, a pinch of cream of tartar whipped with the egg whites will stabilize your creation.
Next to copper, stainless steel should be your first choice. Aluminum grays the eggs. Plastic is too porous, and fat can easily lodge in it. Porcelain and glass have relatively slick surfaces that can slow down the whipping process because the egg whites tend to slip down the walls of the bowl with too much ease.
Whatever the bowl's material, it should be round-bottomed. This increases the likelihood that all the albumen will get its fair share of time in contact with the mixing blades. If you use an electric rotary mixer, be sure its blade moves around the bowl, at least to some degree. Fixed rotary blade mixers whip foam unevenly.
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