Smoothing the rough spots
The first time I noticed the smoothness of a foot, it was one of Martha Grover's pots. Ooohhhhh, wowie!!! Silky, smooth, lovely. Shortly thereafter I learned that Martha used a bit of wet sandpaper under water to smooth the bottoms of her pots. I immediately went to the local hardware store and bought all kinds of sandpaper, sanding foam blocks and whatever else seemed to be worth trying.
If you are familiar with Martha's work, you'll understand why she has to hand sand each pot. Her forms undulate and move, so there is not a strictly flat surface with which she could just apply a block sander or mechanical sander. It's very possible she has found some way around it, between her and her husband, they're very clever, so it may be that she's found some way to ease this task.
My work is mostly wheel thrown, and my feet are entirely flat. I knew that using sanding blocks would work, but it takes an immense amount of elbow grease to get a kiln load of pots sanded. Fortunately, there is a faster way. However, user beware, this takes some practice and MIND YOUR FINGERS!
A few years later, I read this blog post by Jeff Compana. Jeff was, like Martha, a resident at the Archie Bray Foundation. Jeff's pot feet were like glass. Flawless, smooth, shiny. He'd kindly written up this post, which I am somewhat repeating here, I purchased the same grinder and the same disks from the same supplier that Jeff mentions. My set up is outside, and my water regulator on my grinder doesn't work, so I've gotten a bit creative with the process. I don't know what I'm going to do in the winter, but this should get me by 7-8 months out of the year, anyway.
I also thought you might enjoy this Hyperlapse of the grinding set up in use.