I bought the ones from IAP and they are not curved, and they were very expensive... I tried carefully bending one (they seem to be made of brass) and I was afraid it would break, but I was able to get some curvature. Now the cloisonee is starting to pop off where I bent them. I used black silicone caulk behind them to fill in the lack of curvature and it worked OK. I gotta say for the kind of money I paid, they should have the proper curvature.