As I gradually replace my emptying OEM cart with cart filled with Cone's K3 pigment, each of those Epson still have about 10-15ml left in them (15-20% or so). Is it possible for me mix them in my cart which is filled with Cone's?
It is possible, but not a recommended practice. You would be creating your own chemistry at that point by mixing them in the cartridge.
Thank you, I guess I'll discard them.