Antique Russian 18th-19th Century Brass Quadriptych Icon

Authentic antique 18th - 19th century Russian brass and enamel 4-folded panel icon "The Twelve Principal Feast". 
The left fold depicts The Annunciation, The Nativity, The Nativity of The Virgin, and the presentation of the Virgin to the Temple; on the top is The Crucifixion surrounded by St. Martha, Mother of God, Saints John, and Longin Centurion. 
On the right fold are: The Presentation of Christ to the Temple, Baptism, Transfiguration, and Entrance to Jerusalem. 
On the top: the New Testament Trinity God Father and The Son sitting on the throne, and the sphere with a cross between them, above The Holy Spirit in the image of a dove with symbols of the evangelists below. 
Third fold: The Resurrection (The Descent into Hell), The Ascension, The Old Testament Trinity, The Dormition Mother of God of Tichvin with selected Saints; Mother of God of Vladimir with selected Saints; Mother of God of Smolensk with selected Saints; Mother of God of Sign with Selected Saints with Praise of Mother of God - on the top. 
The Calvary cross on the backside.

MEASUREMENTS: Open: Overall length: 35.4 cm. Height: 15 cm (13.94 inches x 5.91 inches).
CONDITION: It is in good condition, showing signs of usage and wear.
Since the market is flooded by reproductions of the Russian brass Icons, which for inexperienced collectors look the same as the authentic objects, we would like to inform our clients that this is a genuine, authentic antique Icon accompanied by a Certificate of Authenticity.
REFERENCES: Similar icons are in the following collections:
1. Smithsonian Museums in Washington, DC (former Kunz Collection) Published in the catalog "Russian Copper Icons and Crosses from the Kunz Collection: Castings of Faith" by Richard Eighme Ahlborn and Vera Beaver-Bricken Espinola on page 47,  No 9.
2. Andrei Rublev Central Museum of Ancient Russian Culture and Arts. Published in the catalog "Crosses, Icons, Hinged Icons" by Gnutova, E. Ya. Zotova on page 128, No 238.