I’m using the right printer that you recommend but its still not black enough to make a good positive. How come?

The problem may not be with the media or the printer. It might be that a third party RIP is needed. For example, Epson 7800 used Ultra Chrome K3 pigment based inks. Our AccuArt3 works very well with it only if a third party RIP is used with the printer. Think of the RIP as a fine tuner and brains for the printer. It will tell the printer how much ink has to be deposited along with a lot of other commands. In my opinion, all professional ink jet printers need a RIP.