Glittering Ruby

 are crafting materials that are dropped by Flamegem Construct and are used to craft Ruby Plate Mail.

In order to get the 50 materials needed to craft the armor you need to defeat the boss up to tier #15. In order to gain the additional 50 materials needed to craft the plus version of the armor you need to defeat the boss up to tier #43.

This material can also be obtained by summoning Famine at the Summoning Stone. If the Boss is active, it will cost 11 gems; otherwise, it will cost 30 gems.