I can tell you that the newly manufactured aprons I and my brother masons use these days in the US (NY State) are not Lambskin but some other thicker leather with a white finish- the NY apron presentation lecture begins "I now present you with a lambskin or white leather apron". I think the change of material is because lambskin is not an easy leather to work with being a weak hide that can stretch out of shape and delaminate- with age the surface flakes and peels away. The higher grades of apron worn by Grand Lodge officers may have real lambskin in them.