Interesting demo of metal causing DOS

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topofmurrayhill

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We use distilled water to avoid metal ions that can act as catalysts for oxidation. Saying they catalyze it means that they are not used up in the process of causing DOS, so they can continue doing damage indefinitely. And they are very good at it.

The most common damaging metal is probably iron. However, copper is one of the worst. The boring bar pictured here was from a tiny batch I made only to test a recipe. It was made with distilled water, but no stabilizers. Another thing I was trying out at the time was a radius plane to create the smooth edges.

What didn't occur to me is that the metal guide that I had to run the soap against was made of brass. That's an alloy of copper and zinc -- very bad. In the photo you can see how the DOS on this bar actually follows the scrape marks from the brass guide.

 

KristaY

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What an eye-opener, TOMH! I've always been very careful to make sure my utensils and curing area are free of metal coming in contact with my soap but I never gave a thought to my mandolin. Granted, I use it once in a blue moon, but now I need to investigate what metal the blade is made of. Thanks for sharing!

ETA: How old is that bar? I'm just wondering how long the DOS took. Also, when did you plane it? Right after the cut or sometime later? I'm just thinking about what stage of cure it was in. Another thought I had was the exposure time of the soap to the metal. When you bevel and plane it's in contact for such a short period of time as opposed to sitting on a metal rack for several weeks. Very interesting!
 
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topofmurrayhill

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What an eye-opener, TOMH! I've always been very careful to make sure my utensils and curing area are free of metal coming in contact with my soap but I never gave a thought to my mandolin. Granted, I use it once in a blue moon, but now I need to investigate what metal the blade is made of. Thanks for sharing!

ETA: How old is that bar? I'm just wondering how long the DOS took. Also, when did you plane it? Right after the cut or sometime later? I'm just thinking about what stage of cure it was in. Another thought I had was the exposure time of the soap to the metal. When you bevel and plane it's in contact for such a short period of time as opposed to sitting on a metal rack for several weeks. Very interesting!
It's pretty remarkable that one or two passes over brass can cause so much damage. However, bad as iron is, multiple sources indicate that copper is MANY times worse. This certainly makes the point. Paranoia is probably called for when it comes to water or oil that has come into some kind of contact with copper or brass.

I don't know how long it took for the DOS to manifest, because I stashed the soap away and didn't look at it for a while. My test batches are 2 bars and the other one was used for testing. The soap was made about 7 months ago. It uses only stable oils, it's about half saturated fat, with iodine 47 and INS 160. It was unmolded, cut and planed after about 24 hours. A soap like that you can unmold while it's still warm and use it within a day or two.

Your mandolin probably has a good stainless steel blade, which should be fine.
 

KristaY

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You're right - stainless steel. Luckily I keep it stored in it's original box so it was a snap to find the "stainless steel blades" on the packaging. I probably noted that when I bought it a few years ago so, good for me, lol.

This is just another reminder that if you don't know for sure it's stainless steel, don't use it, no matter how insignificant it may seem at the time.
 

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