Rare 1940s William Spratling Aztec Hummingbird Chupamirtas Brooch Pin

William Spratling (1900-1967) was an America silversmith who moved to Taxco, Mexico, and was credited with the Neo-Aztec movement in Mexican silverware. His works are hard to find and collectible.
 
This pin is signed SPRATLING OF MEXICO – SILSON INC in a circle logo. In the center right of the logo is stamped ‘AT. PEND.’ which we believe translates as ‘PATENT PENDING’. The patent for this particular brooch design was issued in 1940 and subsequent pieces included PATENTED on the foot to the right of the stamp on the back.
 
The design depicts two hummingbirds (chupamirtas) with outstretched wings. It was created in collaboration with Victor Silson, another American who moved to Mexico and partnered with him in 1940-1942.
 
We believe it is of mixed metals with sterling silver plate as described by the only other person selling one of these online, who explained that silver was hard to come  by in the 1940s due to its need in WWII efforts. Also, Spratling’s sterling silver products were usually stamped 925 or 980, which this one is not.
 
It is in excellent vintage condition, with a nice patina. 
 
We found this in our grandmother’s jewelry collection and can only presume she bought it in Mexico in the 1950s or 1960s.
 
H 1 3/4” x W 3” 
Approx 0.9 oz (25g)