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Help! MdC soap corroding tin.

sarimento1

Contributor
OK, soap chemists, what is cause for rust building up on my Martin de Candre shave soap tin?
3 yrs ago, I repotted some soap from the MdC original glass jar, to a smaller 2-oz flat tin with tin screw top lid. Good for travel.
But the rims in both the bottom and top are now rusting.
No similar issue with any other soap in similar tins.
Any explanation??
 
Are you talking specifically about the lid? Tin rusts, I've had this happen with other store-bought tins I used for Haslinger pucks. I leave my MdC uncovered and the lid packed away dry for this very reason.
 
if it's tin, the tin got wet and rusted. it's common, even if your first experience. that's why I went to Ikea Grundl stainless containers. 7-8 years later, they're just fine in a humid environment.
 

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Another company's tins rusted on me; switched them into great plastic containers. Happens.


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sarimento1

Contributor
thanks, gents, for the thoughts.
i have perhaps a dozen of these tins with various soaps, same drawer, and only the MdC has begun to rust.

various tins.jpg

So, I was wondering if there was anything unique about the MdC.
Anyway, I found some plastic flat-top jars, about same size, and have re-potted. both from specialty bottle.
but, i'll check out the ikea stainless ones for future.

tin vs pet.jpg
 
Some metal jars are tin plated over mild steel. If the plating gets damaged, they can rust. If using one of these for soap, it's always a good idea to let it air-dry thoroughly.
 
but why has only the tin with MdC shown rust?
I'm not sure, maybe the MdC retains more moisture, so when the tin is closed it rusts? Or that tin got scratched somewhere along the line? MdC has a really short, basic ingredient list so I don't think there is anything in the soap to cause that.
 

sarimento1

Contributor
I'm not sure, maybe the MdC retains more moisture, so when the tin is closed it rusts? Or that tin got scratched somewhere along the line? MdC has a really short, basic ingredient list so I don't think there is anything in the soap to cause that.
maybe the MdC has a high residual alkalinity?
 
I seem to remember reading somewhere the MDC owner/soap maker recommended leaving the soap uncovered after use for some time to make sure it’s dry. Maybe there’s a connection to what you’re experiencing. I leave my jar uncovered for some hours before I put the lid back on. Never had a problem. BTW, my jar is from 2010 and still shaves like new.
 
Sarimento1, there is a chemical reaction that occurs when an alkaline substances like Sodium Hydroxide and Potassium Hydroxide come in contact with tin which creates a white, granular substance that can be commonly found on batteries which use potassium hydroxide to make them work. There is also a chemical reaction that occurs when tin comes in contact with water and oxygen which is rust. So, unless a special coating is applied to the container by the manufacturer these can occur and if you keep and use a product for a long time without the coating then there is more chance that this will happen so keep that in mind!
 

sarimento1

Contributor
...There is also a chemical reaction that occurs when tin comes in contact with water and oxygen which is rust....
Smarty pants chemists!
Nothing had appeared on my tins until that past year, now starting to show!
Looks like I'll be re-potting them into aluminum or plastic!
Thanks, Dave!
 
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