As it has been said, it is made with tailoring.
You need
- 1 crystalline swatch (made with 2 crystalline silk)
- 1 mantle pattern
- 1 silver thread (bought in Thurgadin)
I am not 100% sure but I think you need a Coldain Sewing Kit (also bought in Thurgadin) to combine that.
If zoonfactor found that in Erudin I think it's because someone sold it to a vendor while practicing tailoring. I do that a lot. You just can't try to find players to sell your armor when you make 150 pieces in a row! :)