A close look shows that the use of ColorLok technology does have an impact on output quality, especially in duplex mode.Paper is usually the overlooked factor in office printing. That changed two years ago with the advent of ColorLok technology, which has since been adopted by a list of paper vendors.

Does it make any difference?

The theory behind ColorLok, presented in an HP backgrounder, is based on the fact that pigments in inkjet ink are suspended in a clear liquid called the ink vehicle. The pigments have a negative surface charge, and when they come into contact with salts that have a positive charge the pigments flocculate, meaning they come out of suspension. So the idea of ColorLok is to salt (pun!) the paper with positively charged salts to encourage flocculation.

So when the ink encounters the salted paper the pigment immediately leaves the ink vehicle and remains on or near the surface of the paper. The rest of the ink may continue to diffuse through the paper, but it will not take the pigment with it.

The result is supposed to be sharp, vivid color since all the pigment is on the surface, and there is no feathering as the ink diffuses by capillary action. And the image should not show up on the other side of the paper, leaving it pristine for duplex printing.

To test the theory, I printed out the same page (containing text and some color images) using an aging HP Officejet 7210, which can use all the help it can get. I used two ColorLok papers: 24-pound 97-bright HP Bright White Inkjet, and 20-pound 96-bright HP Multipurpose. For the opposition I used 20-pound 92-bright Georgia-Pacific Copy & Everyday, and 20-pound 94-bright Caliber Multipurpose Tree-Free. (The latter is 70 percent sugarcane and 30 percent bamboo.) I also found some old 100 percent cotton 24-pound Resume Paper.

At first glance, in average lighting, I could see no particular difference. I saw no smudging indicating that the ink was not drying fast enough. None showed any of the feathering that ColorLok is supposed to suppress.

Under a bright light, the two ColorLok papers produced colors that were brighter than the Caliber paper, although this was most noticeable when they were held side by side. I could not see much difference between the ColorLok papers and the Georgia-Pacific paper and the old Resume Paper.

Turning them over, the contents of the graphics were immediately evident on the three non-ColorLok papers. This would be a problem with duplex printing. The graphics were a little less evident on the 20-pound ColorLok paper. Their presence was not immediately evident with the 24-pound ColorLok paper, and would be a non-factor in duplex printing.

The difference between the Resume Paper (where the graphics showed through) and the 24-pound ColorLok paper (where they did not) was especially notable, as they were both 24 pound. So ColorLok would seem to be a better choice for duplex printing.

Basically, they all sufficed for everyday one-sided use, and no details were lost. The 24-pound HP ColorLok paper came out best overall, being brighter and heavier and having the least effect on the reverse side. The old (and expensive) cotton provided an old-school feel that the others can't match, but would not be as suitable for duplex printing.