Any Chemists Know What’s Going On Here?

Here is what I posted last night but wanted to see if I can find out more. After posting this image, I wasn't sure if when Plisson started whether they used badger or boar bristle. I will send them a message on IG to see if they will share.

Thanks for the information - I'll try to clean it with salt and lemon juice.  I think its reacting with something in the MDC soap because I use the bowl almost everyday and it doesn't do that with any of the other soaps I use.  I haven't used MDC in a long time.

Ketchup, yes ketchup, let it sit for a couple of minutes and wash it with soap and water. You'll be amazed.  

The acid in the tomatoes?

I assume so, and there may be some vinegar in it as well.

According to Hoyle... I mean Heinz...

According to Hoyle... I mean Heinz...

Ah, must be the "natural flavors". 

Yes ketchup will work quite nicely.

Tomatoes contain several acids with citric acid and malic acid being the most common. In making ketchup, vinegar and salt are also added. The key thing is that the acids are all organic acids. Inorganic acids like phosphoric, nitric, hydrochloric, and sulfuric acids might be too strong and damage the copper.

If MdC contains sodium chloride, it can definitely react with the metal. I checked though some of the ingredient lists for my soaps and found that DR Harris, Mitchel's Wool Fat, Pre de Provence, and Williams Mug Soap also contains sodium chloride, so they might do the same thing. I did not find any artisan soaps that use sodium chloride. Perhaps sodium chloride helps harden the soaps, but not all hard soaps use it.

Pretty normal once the lacquer has worn away. That happens to mine when I leave excess soap pressed into it for more than a day. Usually cleans right up after a couple of uses though. While the copper bowls are beautiful, it's one of the reasons I use my HC&C stainless bowl more often.

I tried the ketchup and after about 5 minutes it had cleaned most of the staining off. It probably would have got it all if I’d left it longer. I then tried lemon juice and kosher salt and it got the rest off. The scrubbing from the coarse salt helped.