Source: Period dictionary
Song kiếm (雙劍) means double sword. They are a rare variety of Vietnamese straightswords, kiếm (雙劍), with two blades that fit into a single scabbard.
A rare set of full-length song kiếm. Sold by Mandarin Mansion in 2019.
Most song kiếm are relatively short, full-length ones are extremely rare. I briefly owned the set above, and the only comparable set known to me at this point is in the Metropolitan Museum, accession number 36.25.1452a–c. (Bequest of George C. Stone, 1935.)
Since the song kiếm (雙劍) was not an emblem of rank like the standard single kiếm was, they tend to be of more sturdy built with actual use in mind. Where most Vietnamese kiếm have hilt mounts made of silver sheet with resin inside, it is common for song kiếm to have hilt mounts of a contrasting metal. Often, stronger brass or another copper alloy, and sometimes even iron is seen.
A very good set of short song kiếm. Copper alloy hilt mounts, ivory grips and silver scabbard mounts.
Notice the very nice heat treatment on the quality blade. Ex Philip Tom collection.