A customer wants a cookie sheet that’s thick, without wired sides, short sided, and copper with a tin lining. The most important part? 90-degree square corners. I didn’t ask why, but I started to see what could be possible.

There are two ways to make baking sheets with tight corners. The first is to do it seamlessly. This requires a sort of lopsided upside-down W to be cut into the corners. The sides of the pan are folded up, which inadvertently creases the W so it’s squished together. That excess material is further folded together and then off to one side of the pan. You may actually see this on some basic baking pans or square or rectangle cake or brownie pans – if you look at the outsides of the corners you’ll see the sheet metal has been folded up (if the piece isn’t stamped—if it is stamped it will have no seams at all).

The other way to make baking sheets is to have a seam in the corners. This is likely what I will have to do because the pans will be made of quite thick copper and I won’t be able to bend the corners well to do seamless. However, the tinning of the inside of the copper sheet will automatically seal up these corner seams and they’ll be nice and square. The corners will be straight on one side with a tab that bends in on the other. My dear friend Julia of Design Between has been working on the renderings for me – we aren’t quite there on the corners, as I need the tab to be more of a half-triangle than a circle shape in the bottom corner – but we’re close! My hope is to get these mass-stamped and then will have to bend them individually on the bar folder and tin them up over the fires.

It’s always an adventure in the copper shop! But now you know the two types of corner seams!