I have been on the lookout for a copper bowl for the last couple of years. It started with our waffle recipe that says to "beat egg whiles until stiff peaks form". Years ago I would whisk the egg whites in a glass bowl for 20 minutes until I was ready to collapse, and still the egg whites would never form stiff peaks. Later, I started watching the old Julia Child show, "The French Chef", and reading her book, "Mastering the Art of French Cooking". She goes through an exhausting explanation of how to whisk your egg whites such that stiff peaks form:
1) The egg whites will fluff best if they are at room temperature. I usually put the egg whites in the bowl, and I put the bowl in tepid water for a few minutes to bring up the temperature of the eggs.
2) Any traces of oil will prevent the egg whites from fluffing properly, so be sure that the whisk and bowl are "impeccably clean". Traces of egg yolk in the egg white will have a similar effect, to be sure not to let any egg yolk (or shells) find their way into the egg whites.
3) The type of bowl is important. People that need to fluff egg whites know the mysterious secret. A copper bowl fluffs egg whites better than anything else. A copper bowl tends to be prohibitively expensive ($100 or more at Williams Sonoma), so a stainless steel bowl is the poor man's alternative. A glass bowl is particularly bad, because it is too slick and as you try to whisk the egg whites, the whisk pushes the eggs around the bowl instead of chopping through the egg whites.
For the last few years I have been making waffles using a stainless steel bowl to whisk the egg whites. Stiff peaks always form, but just barely. It has worked pretty well for me, and the resulting waffles are light and fluffy. Yesterday I found the copper bowl I've been looking for at T.J. Maxx. It's a little on the small side, but it works. I beat an egg white, and perfect stiff peaks formed, in fact it quickly went beyond stiff peaks so that the egg whites almost looked like Styrofoam. It quickly confirmed that copper bowls are, in fact, a critical factor in beating egg whites.