What’s the difference between ink jet inks that contain aqueous dyes versus aqueous pigments?
Aqueous Dye: The aqueous in aqueous dye and aqueous pigment refers to the fact that water is the main liquid vehicle for transporting the dyes and pigments to the printed page. With both types of aqueous inkjet inks, the water evaporates and leaves just the colorant. The difference in particle size means that dye-based inks have some benefits over pigment-based inks. The main benefit is that the small particle size allows light to bend around the dye molecules, which results in a color transparency that gives prints made from dye-based inks a larger color gamut than prints made from pigment-based inks. The small particle size also allows dye-based inks to more easily permeate porous surfaces and substrates and not simply lie on the surface, as is common with pigment-based inks. On the negative side, dye-based inks are more susceptible to moisture, impermanence, and fading. You do not want to get a dye-based inkjet print wet. The dyes will be more easily dissolved from prints and parts of the image could be removed.
Aqueous Pigment: For those of us making photographic or fine-art prints, we want our prints to last as long as possible, so we choose to use pigment-based inkjet printers and inks to give us better longevity and fade resistance. Despite the loss of color gamut with pigment-based inkjet output, the increased longevity for us as photographers is worth it. That being said, the ink manufacturers do things to help increase the color gamut from pigment-based inkjet prints. The first thing they do is to mill the inkjet particles to be an order of magnitude smaller and a more uniform size (100 times larger, not 1000 times larger than the dye molecules). This increases the ability of light to bend around the particles, the color transparency and, therefore, the color gamut. They also mill the pigment particles so that the larger pigment particles will not clog print head nozzles. In the case of Epson UltraChrome ink technology, Epson, also, encapsulates or coats the milled pigment particles with a resin, which allows even more transparency and color gamut from the resulting prints.
Tom P. Ashe. Color Management & Quality Output: Working with Color from Camera to Display to Print. Focal Press, 2014.
I would also add that it’s a good idea to stay with “name brand” inks instead of third party inks. They are of much better quality and for such a critical component of your work it’s not worth risking the archival integrity to save a few dollars. Jim Kedenburg