Daily Tedium

Rough Edges

Why ceramic coffee cups have a spot at the bottom that’s rough to the touch, despite the rest of the cup being glossy. It's kiln you that you don't know.

By Ernie Smith

This sounds strange to think about, but when it comes down to it, there’s often a reason for everything, even if you’ve never even pondered it before.

Case in point: Have you ever wondered why traditional ceramic coffee cups, which are smooth around the edges, have that rough circular spot on the bottom? That was not a happy accident—it was a design choice.

See, that squat ceramic coffee cup, the one you’ve seen millions of times, in diners and living rooms, sometimes with brass-knuckle designs, came from somewhere—specifically Victor, New York, a town that initially made its name building porcelain insulators in the late 19th century.

Victor Insulators got into coffee cups not because it was a passion of theirs, but because insulator sales slowed down, and, more importantly, the times demanded it. During World War II, the U.S. Navy requested a contract for a coffee cup that was thick, well-designed, and didn’t have a handle that could break off. (These things were on ships, after all.)

Victor, which already had a sizable porcelain business (as well as an underutilized factory), was in a position to help. As a part of the process, of building to military specs, the company stumbled upon perhaps the most subtle part of the design: Before putting a piece in the kiln for 72 hours, it wiped off the edges with a piece of rubber, a process called dry-footing.

The reason for this is simple: If it didn’t have that rougher matte-feeling area, the glossy ceramic would stick to the shelf of the kiln while being heated. A manual for a kiln on Google Books, easily the most riveting source I’ve ever linked to, explains exactly the process for doing this:

You can prevent glazed pieces from sticking to the shelf or kiln bottom by “dry footing.” To “dry foot” a piece, remove all glaze from the portion of the piece that will rest on the shelf. Using a wet sponge or a piece of grit cloth, clean off the glaze from the bottom of the ware and slightly above the base so that it will not run down and touch the base. Do not use dry footing for low-fire glazed pieces that will be placed in water while used or cleaned.

This design feature, which also helps the cup’s stability, wasn’t unique to coffee mugs, of course. It’s the kind of thing you might find on a vase, a plate, or an heirloom.

But this use case helped make the cup even more useful, ensuring its long-run status as a coffee icon—especially after World War II, when the cup regained its handle and permeated American society. (The Huffington Post has a great 2015 article explaining how the Victor coffee mug took over diners across the country.)

Victor Insulators is dead—it faded from view in 1990, leaving behind a long legacy. And that legacy, strange as it sounds, was never completely smooth.

Just mostly smooth.


Ernie Smith

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Ernie Smith is the editor of Tedium, and an active internet snarker. Between his many internet side projects, he finds time to hang out with his wife Cat, who's funnier than he is.

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