Thank you very much for your replay
The concentrated solution of potassium hydroxide (KOH) was used for soft and liquid soaps.
I am talking only about traditional hard/bar soap that was made using sodom hydroxide (NaOH) and sea salt concentrated solution. Temperature maximum of 120°. Copper cauldron can be used in this case too?
Traditionally, stone or copper was used for the making of relevant cauldrons, later - iron or cast iron, today - stainless steel, best considered AISI 430.
I am interested in if there is a better modern material.
As for the copper cauldron, kindly tell me which company is making it?
I did not find such a company.