Quote Originally Posted by mrsell63 View Post

This particular soap contains natural tallow which is good for leather and I use it on one particular horsehide strop. Haven't noticed any thing on the strop surface that would upset me. Seems to work fine.
Sort of...
Soap is made by the chemical reaction of fat (and oil) with alkali.
The generic reaction is saponification and the end product is soap.
When done correctly there is no alkali (lye) and no fat (tallow) left.

See: Saponification - Wikipedia, the free encyclopedia

Since alkali is so hard on skin 'people' soap including shave soap
is hyper-fatted. Laundry soap and other "cleaning" soaps are slightly
rich in alkali and the alkali can react with grease and oil.

One interesting name game is Mitchells Wool Fat Shave soap.
By most measures lanolin is not a fat and is not saponified in MWF
but added as a conditioner to a well balanced tallow based soap.

Subtle but important.