I second the idea of not to overclean. The age is part of the appeal.
The Ngombe tribe forged these swords and traded them widely, to friends and enemies alike.
The name Ngala was used by early colonial authorities to describe an ethnic group that they imagined lived upriver from the capital. The name Ngala figured prominently on early maps and is today considered one of the three main regions of the Democratic Republic of Congo. In that area, however, many tribes are to be found. Collectively, many of these tribes belong to the Mongo ethnic group.
I own several of these swords. One is definitively identified as collected from Bangala (Ngala), the name of a station on the Congo River and also a dialect of the Mongo people. This sword was originally collected by a Belgian missionary, the uncle of the previous owner, in the Belgian Congo in the early part of 20th century.
http://atkinson-swords.com/collectio...ord-congo.html