Dimiscarene blades are expensive Arridi swords made in Dimiscar. Selethen explains in The Emperor of Nihon-Ja that, "Our swordsmiths in Dimiscar developed a similar technique for creating extra-hard blades many years ago." This technique talked about Selethen is compared to the Ranger smiths' way of developing their far superior steel/iron.
This is a reference to "Damascus steel," a real material.