Cortosis is a material that is known for its rare property to either deflect or shut down a lightsaber depending on how refined and the amount used. Cortosis was difficult to mine not only due to its rarity, but also the fact that unrefined cortosis was an energized material that could kill organic life who touched it. This includes even the large Hutts. Cortosis miners had to wear pressureized sealed suits since particles of the material would cause hair loss, sickness and death. Due to its effectiveness against energy weapons, plasma cutters and similar tools were of no use to brute for hydraulic jacks were needed to pry the materials loose and even this was made harder by the fact that cortosis dust would clog the machines.
Once extracted and refined though the results were without question. Cortosis was used during the days of the Old Republic by using as little of the material as possible to give Republic soldiers vibroblades that could withstand Sith lightsabers.
Darth Desolous used a shield made of cortosis during his attack on the Jedi.
During the Clone Wars the CIS were known to be excavating a cortosis deposit on the planet Bal'demnic. Quinlan Vos was know to wear a cortosis gauntlet during the Clone Wars.
During the years of the Imperial Remnant, Galak Fyyar utilized cortosis in his Shadowtrooper project, constructing an entire suit of cortosis for this elite unit of Dark Jedi for Desann's Reborn project. They were used against Kyle Katarn and later took part in Desann's final attack on Luke Skywalker's Jedi Academy on Yavin IV.
Over a hundred years after the original Empire fell, the New Empire utilized Imperial Knights, who wore red gauntlets, using them in their many battles with the One Sith.