International Masons leather apron.
A white leather apron edged in blue, with International Masons symbol (Square & Compasses above a key), all-seeing eye on flap.
Apparently a standard 3° member’s apron.
I bought this on eBay as a lot which included the fez, an Intl Masons apron, and another apron. See TAFC.2009.17 & .19