When I bowl lather - about half the time - I use the bowl on the left in the pic. I saw another member here using it and really liked the looks, and it performs beautifully. The craftsperson is in Israel, I think - she sells them on ETSY.
A soup mug or any other bowl that is about 2.5 to 2.75 in at the bottom and about 4 to 5 in high is ok. Anything that YOU feel comfortable whipping up your lather is fine.
Any bowl that you can comfortably nest in your palm wrap your fingers around or has a handle is a good thing to have.
Georgetown Scuttles beat bowls every time, adding heat to the great lather. However I have a Japanese bowl actually meant for grating wasabi, that lathers like crazy. I'm just afraid it's too rough for a good badger, so I reserve it for my boar, which I don't use.
I use (not often) a rice bowl I bought from Target because it has a lid and a lip to prevent lather from pouring out. Then I started to use a cereal bowl I got from Walmart because I loved how it looked and it was nice and big. I now exclusively use my George Town Scuttle... Love that thing!!!! Best investment I have made.
Stoneware cereal bowl I grabbed on clearance at target for about 4 bucks. It's large, but fits my hands well and allows me to really agitate that lather without sending it all over the bathroom.
I use an Edwin Jagger RN6 bowl most of the time, others a buffalo horn bowl. The Buffalo horn bowl makes fantastic lather, but the RN6 transfers heat better
I have used bowls and custom potter scuttles ect and They just don't transfer heat as well as soapstone. I looked everywhere and couldn't find what I wanted so I made my own out of soapstone I have tried several colors and harnesses , the heat transfer is amazing!!! The small bubbles balloon and the foam is super warm. It works so good all my friends want one and I have done over ten. Try it soapstone is the secret thin wall no more than an inch.