I have been considering making soap.
I often wondered since there wasn't any lye back in those times how the ash made soap. I found this online- so now I know!
I've never found that salt does squat for hardness (unless I'm making a salt bar where the salt is in huge quantities). Salt was used way back when sodium hydroxide wasn't available and people made their own caustic out of ashes - but that was potassium based caustic. Then salt was boiled with the soap to convert the potassium salts of fatty acids (soft soap) to sodium salts.