I'll guess that a collectable mug is one that is probably old and rare. But what makes a really good one? I have a couple of inexpensive Turkish copper mugs that do the job, and clean up easy. What do you look for in a mug?
Get a mug that is wide enough to hold the puck at the bottom and still give the brush room to swirl. You don't want to be clanking your brushes on the sides of the mug.
I melt (TSD soaps), press (Stirling soaps), or just set (Tabac soap) into a small clear bowl - used to be 3 for a buck at the Dollar store. I load my brush from there, then whip up the lather in a mug. Those mugs meet the parameters Primotenore mentions. Most of what I have are low, wide coffee mugs and soup/chowder mugs.
Except for creams, I use wooden bowls and Old Spice mugs for my soaps and lather directly from them. Old Spice mugs work great and holds the puck of soap in place. If you want an Old Spice mug, PM me your address and I'll send you one.
I use to go to Good Wills, Salvation Armys and yard sales for things to to use as shaving mugs ....... now I palm lather or face lather, no need to have a mug.
If you are occasionally clumsy like I am don't use a glass or ceramic lather bowl/mug. I dropped one in my bathroom and took me 30 minutes cleaning it up before I could finish my shave.
I use these (see pic), and they all work fine. My favorite is probably the little kids cereal bowl with dancing penguins on it that I bought at a convenience store in Japan because of its shape, and my least favorite is the huge "Intergalactic Indestructible Shatterproof Travel Scuttle" by Phoenix Shaving which is irritating to use in practically every way (and is a hassle to clean), but warm shaving cream is nice in the middle of winter and it will have to do until I find a ceramic scuttle I like. The Dirty Bird pottery shaving bowl is pretty cool. I used to think that the size or texture of the mug had a lot to do with its ability to whip up cream. I've since decided it doesn't matter what kind of mug you use, it's your technique that matters most. At least half the time these days, I lather on my face, though. I'm currently on an efficiency binge, and face lathering entails less waste then using a bowl. - Bax
A good mug is wide and short. Old spice figured that out quick. If they are wide and tall, a person can drop in a hockey puck to raise the soap up. This works on the 100+ gram (3.5 oz.) soaps and the mugs those fit in.
i use my trusty captain's choice heavy copper bowl most often,it will hurt a toe when dropped,but that's about it..
I used a small salsa bowl from a Mexican restaurant once. That was interesting. And it worked great! - Bax
Better options are always available. BUT, better is comparative. To the brush. The sizes of the brush demand the sizes of the bowl or scuttle or mug. Just Physics!!! What I'm sure of, lines and ridges and bumps have (mostly) aesthetic porpouse ...
