Dark Glass

Ok. I assume if you're here, you know about the Golden Throne. Especially the part about its functions as a Webway portal. The Dark Glass is its prototype.

The only significant part it played in the story arc was that as the White Scars, during their gurellia war, were encircled by the traitor legions, their chief Stormseer opened a Webway portal with the device, allowing them to escape and join the Siege of Terra.