Early 20th century diamond and sapphire square cluster ring

Weight: 4.5g, the oblique cut-corner square centred by a principal round brilliant cut diamond, to an accent border of calibre cut sapphires, outer frame of single cut diamonds with pierced Greek key band in between, similar to gallery, diamond line shoulders, all stones millegrain set, reeded shank.
Length corner to corner 1.8cm / ¾''