crock pot

I have searched this high and low on the internet and this forum and have not found an answer anywhere...maybe because it doesn't matter and you can use any of them. My question is for HP and making liquid soap in a slow cooker, should the inside be made of ceramic, stoneware, or apparently...

I take bacon grease from the kitchen where I work and use the crock pot hot process method to turn it into soap. I work at a fat discount to ensure complete saponification. I will generally start a batch in the morning, let it boil for a while, turn off the heat, and then bring it back to a...