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Brass stamp discolouring soap!

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laurauk

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Hi I have a brass stamp which I love how it looks like, however certain soaps, particularly whites/clear ones the stamped area starts discolouring after a few weeks, becoming an awful yellow and spoiling the bar 😔.

Any idea why this happens? Any suggestion to fix those soaps? Desperate for help, thank you for reading!
 

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AliOop

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Pretty bars and pretty stamp! Unfortunately, that looks like DOS to me - dreaded orange spots, a form of rancidity. One of the causes is contact with metals, including anything other than stainless steel, such as brass.

If you want to use that stamp, you will have to line it with plastic cling wrap so none of the metal touches the soap.
 

TheGecko

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"Brass is a metal alloy that is always made with a combination of copper and zinc. By varying the amount of copper and zinc, brass can be made harder or softer. Other metals—such as aluminum, lead, and arsenic—may be used as alloying agents to improve machinability and corrosion resistance. "

Aluminum and Sodium Hydroxide are enemies. Even though 99.999999999999% of the lye is used up in HP/CP soap, the microscopic amounts left are the reason why folks are told to NOT use metal racks while their soap cures. And since soap is typically planed, beveled and stamped within the first week if not a few days after it has been cut, using anything but Rubber, Acrylic, or Resin is not a good idea.

Because you no doubt really like your stamp, one thing you can do is place a piece of plastic wrap over the top of your bar and then use your stamp. I would recommend using a good quality brand of plastic wrap as opposed to a cheap one and only stamp once or twice as the stamp will eventually wear through the plastic. If that doesn't work well, you will want to have an acrylic stamp made.
 

DeeAnna

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Brass contains copper. Copper is Number 1 of the Ten Most Wanted metals that cause rancidity in fats and soap.

I'm not entirely sure I'd assume plastic wrap is good enough because you don't want even a small trace of copper on soap.
 

Loran

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I know you can get your stamp coated with a clear coat or enamel to seal the brass from oxidating, but I don’t know how the sealant will react with the soap.
 

laurauk

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"Brass is a metal alloy that is always made with a combination of copper and zinc. By varying the amount of copper and zinc, brass can be made harder or softer. Other metals—such as aluminum, lead, and arsenic—may be used as alloying agents to improve machinability and corrosion resistance. "

Aluminum and Sodium Hydroxide are enemies. Even though 99.999999999999% of the lye is used up in HP/CP soap, the microscopic amounts left are the reason why folks are told to NOT use metal racks while their soap cures. And since soap is typically planed, beveled and stamped within the first week if not a few days after it has been cut, using anything but Rubber, Acrylic, or Resin is not a good idea.

Because you no doubt really like your stamp, one thing you can do is place a piece of plastic wrap over the top of your bar and then use your stamp. I would recommend using a good quality brand of plastic wrap as opposed to a cheap one and only stamp once or twice as the stamp will eventually wear through the plastic. If that doesn't work well, you will want to have an acrylic stamp made.
Great piece of information, thank you so much for replying!

Thank you all for your advice. I'll try with cling wrap in a small batch to see results, always good to experiment, but I think I'll order the acrylic stamp to use from now on! Thanks again💚
 
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