How to make extremely hard soap

[DeeAnna]

Thank you for the additional information. It's helpful.

The lye concentration is about 31%, so the water content could be lower. I'd set the lye concentration to 40% for example. But be ready for the soap to overheat with less water -- coconut oil soap tends to get pretty warm during saponification. That said, your batch size is rather small so overheating is less of an issue.

It may seem counter intuitive, but you also want to ensure the soap gets warm enough to go into the gel phase. So too cool isn't good, but too hot isn't good either.

As @ScentimentallyYours mentioned, a soap high in stearic and palmitic acids is going to be a physically hard soap. If you don't want to use commercial stearic acid or soy wax (hydrogenated soybean oil), you might get what you want by making an all-tallow or mostly-tallow soap. Tallow can be harder than an all-coconut soap to the point of being too brittle and hard to cut. You'll also want to use a lower water content and ensure the soap gels.

 

[ScentimentallyYours]

If you don't want to use commercial stearic acid or soy wax (hydrogenated soybean oil), you might get what you want by making an all-tallow or mostly-tallow soap. Tallow can be harder than an all-coconut soap to the point of being too brittle and hard to cut. You'll also want to use a lower water content and ensure the soap gels.

The hardest soap I’ve made was Ben Franklin‘s Crown Soap, of tallow and Bayberry wax. I made a boiled soap version and a cold process version with modifications. The boiled soap version, which I still have some bars of, is hard like a piece of plastic and it doesn’t even dent. I’m thinking the boiled soap process creates the hardest bar of soap, because it removes all of the glycerin.

The super hard, genuine Aleppo soaps are also made from a boiled soap process. @DeeAnna, Do you think a straight tallow soap with a boiled process would work for @Ruth Gregory?

The Franklin soap works well in hot water, which is surprising to me because it’s so hard. I’ve noticed in some carpentry sites that pure olive oil soap is used for some finishing processes, so perhaps a boiled Castile Soap is another option???

 

[DeeAnna]

...Do you think a straight tallow soap with a boiled process would work...

I have no idea; I've never tried it and the soap making resources I have don't discuss this point.

I don't know that I'd assume the boiled method will make a harder soap just because the glycerin is largely removed. Maybe, but a person would have to test to know that. And one would also need to account for the other differences in the soap due to the boiled method versus the cold process method, not just the presence or absence of glycerin.

All I know is a cold-process soap made with a high % of tallow can be extremely hard.