Remember that Castile soap was originally made in the Castile region of Spain using olive oil saponified with lye made from the ashes of "barilla", a name for salt-tolerant vegetation that grew along the Spanish sea coast.
That means the original Castile soap was indeed a 100% olive oil soap, but not necessarily one made with a 100% sodium alkali. The lye would have been a mixture of potassium and sodium alkalis, not a pure sodium alkali (aka sodium hydroxide).
The modern consumer and legal definition of a castile-type soap is a soap made from 100% vegetable oils. The more precise soapmaker definition, based on the historical roots of the word, is that castile is a 100% olive oil soap.
As Zany's pointed comments show, however, you can't assume any particular soap maker will know about this more precise definition of castile -- or if they do know about it, will choose to use the word castile to mean a 100% olive oil soap.
So ... I try real hard to not use the word castile at all, because no one can agree on its meaning anymore. 100% olive oil soap leaves no room for misunderstandings and hard feelings.
That means the original Castile soap was indeed a 100% olive oil soap, but not necessarily one made with a 100% sodium alkali. The lye would have been a mixture of potassium and sodium alkalis, not a pure sodium alkali (aka sodium hydroxide).
The modern consumer and legal definition of a castile-type soap is a soap made from 100% vegetable oils. The more precise soapmaker definition, based on the historical roots of the word, is that castile is a 100% olive oil soap.
As Zany's pointed comments show, however, you can't assume any particular soap maker will know about this more precise definition of castile -- or if they do know about it, will choose to use the word castile to mean a 100% olive oil soap.
So ... I try real hard to not use the word castile at all, because no one can agree on its meaning anymore. 100% olive oil soap leaves no room for misunderstandings and hard feelings.