I made my 1st print with my P800 converted to Piezography Pro using Canson Rag Photographique. I also made the ink switch from PK to MK. I did not see that the GCO covered the image at all. I wasn’t expecting it to be glossy but there is no sign that it printed at all. I pulled the cart to check the level (since I ran an initial fill to remove the PF I had used to clean out the original color ink) and it was more than half full-and primed.
GCO does not print on matte paper. Even if you used a gloss curve it would not make matte paper glossy. It’s a copolymer that is set to gloss out only glossy papers. It isn’t a “varnish” per-say