Varnish (UV).

A clear UV ink laid on its own channel over or beside the colour, for a gloss or matte finish, a protective coat or a raised feel. ONYX classes it with white, metallic and gloss enhancers as a non-chromatic spot ink, kept out of colour management, and its RIP picks up a spot colour named Spot1, Spot2 and so on without extra mapping. The name is per RIP, so the file has to use the one the shop's RIP expects. DTF Transfer Studio notes that PNG and JPEG do not keep named spot channels, so the varnish has to travel as a TIFF or PDF. The Epson V-Series best practices published by Grimco list the trade-offs: varnish is less flexible than the other inks and can chip if bent beyond 165 degrees, heavy varnish shows dust, and a 20-30% layer gives a more matte look while keeping some protection. Their V7000 cures varnish to gloss only. The common fault is a varnish channel that arrives empty or flattened into the colour, so the job prints with no varnish and nobody notices until the customer asks where the gloss went.