There's something else in there other then just the pigment. I say this because if you mix them at about 6 to 1 you get the same consistency of the ink but they don't have that sort of gloss finish that the inks have.
I guess I could try to stick a little Varnish in there but as you said, sounds like a spendy mistake. I'd rather just pay my 3-4 bucks and call it a day.
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GunDown's Hate:
When GunDown fields an army all of his casters generate +2 Focus. GunDown sucks at hordes and therefore ironically, warlocks generate no extra rage and can never get a bonus from cover.