Gem Harnesses are suits worn by their wielders to enhance fighting ability and grant powers. Primarily seen during the Faceless War, they were used mainly by officers, artillery crews and specialist troops. They run on the same technology as the Gem Cartridge.
They are basically one large cartridge system. They are, however, usually keyed to a different type of gem. For example, during the Faceless War, Warlord Singed of Shabboltholm had a platoon of bodyguards that had topaz gem suits and could shield areas dependent on how many were close together. Beatrix had a suit that used special gems that gave her powers like a very large beam (larger than the average diamond cartridge), or allowed her short range flight through a ruby cartridge.
However, after the devastation of the Faceless War, much of the designs were lost, and with the advent of other weapons, that gave the power of a gem harness in a one-handed sword. The technology never had enough interest to reinvigorate production. A few suits are now generally seen among pirates, bounty hunters and high level assassins.