Inkjet Pigments and Color Longevity
Initially inkjet prints in the early 1990s, like the Iris, Epson or HP dyes, utilized unstable dye colorants because that is all that was available. In a broad sense, dyes like used in analogue color coupler prints are smaller and less complex molecular bonds that can fade or shift easily when exposed to daylight or heat over a period of time. Pigments as a class of image forming molecules are composed of much more complex larger molecular bonds that can hold up quite well in daylight and dark storage. Early inkjet pigments could be somewhat dull in comparison to the gamut of dye inks, but that changed about 17 years ago. Amazing progress in both permanence and color intensity has been made in the last decade. But there are different kinds of inkjet pigments on the market today, some of them great, some of them very good, and some not so good depending on what may or may not be added to them. The same goes for print media. Although the HP Vivera inkset has been shown in accelerated tests by several sources, done over at least the last 12 years, to still be the most permanent pigments ever sold for photo inkjet applications, the new Epson HD pigments have increased their durability quite a bit by reformulating their yellow channel, that also effects reds, oranges, and skin tones. As of this writing, apparently the latest Canon “Lucia Pro” pigments have lost some ground in stability from the previous Lucia Ex inks (as published by Wilhelm-Research and Aardenburg Imaging), while gaining some increase in color gamut, at least from the tests published so far. The previous Canon Lucia Ex pigments that we use, are about where the most recent Epson HD inks are in general stability.
In the last 8 years or so, we have found Mark McCormick’s testing at Aardenburg Imaging to be thorough and accurate in many important ways. ( www.aardenburg-imaging.com) His I Metric system relies on modern and disciplined methods that no one else using, because he shows you exactly how light is effecting or not effecting various paper/ink combinations over specific progressions of time. You see from his published color charts what colors are changing at specific intervals, and at how many megalux hours the change is starting to occur (these measurements can be converted to years of display). So we have learned what kinds of papers of various manufactures are working best with what kind of inksets regardless of who manufacturers them. And the corporations are not paying for the tests. This is all difficult to accomplish as the big global companies that make these materials continue to change their inks, and sometimes their papers. But this is a good way to see obvious trends in the industry. Aardenburg has clearly shown the detrimental effects of OBA additives (optical brightening agents) - dye brighteners that have also been used in most all analogue commercial photo printmaking since the 1950s. Other testing labs have not published results so thorough. Small amounts of oba added to the pulp when the paper is made can be considered acceptable, while cheaper oba dyes or those added later to the paper’s coatings can greatly reduce the overall paper luminance when exposed to light or heat. Of course how one cares for the artwork will have a big effect on long term permanence.
The most permanent inkjet papers are the ones generally referred to as “natural”, meaning they contain no brighteners at all, just the natural color of processed cotton or wood pulp. However, many if not most of the photographers out there, especially making color prints, prefer more color and contrast brilliance, thus the popularity of some kind and degree of whiteners in the many of the best papers. This is also true in the analogue photo world and even the intaglio or silkscreen world. The most stable whiteners are actually pigments, not dye based optical brightening agents. Canson and Breathing Color companies use these pigment whiteners as do some of the Epson Legacy Series, based on the long available Canson papers..
One of the things that can contribute to premature color staining and possible image fade is the presence of problem adhesives used in various kinds of print mounting, like rubber compounds, as well as some glues used in the fabrication of some portfolio cases or shipping containers. Even thermo plastic heat mounting (traditional dry mounting) has sometimes shown to be a problem, apparently because the heat generated by the mounting press can cause the release of chemicals that are used in the tissue that effects the inkjet paper coatings. Also the mount being mounted to can be a factor. Archivally inferior mounting substrates, like cheaper foamcor which can have poor ph qualities and other chemicals in the core, or acidic mounting boards, are things to to stay clear of in mounting if long term stability is of a major concern. As far as I know at this time there is no official data that has been published about the detrimental effects of various mounting adhesives. What has been learned has been from word of mouth. Hopefully that will change in the future.
Inkjet media is coated with what is called an inkjet receptor coating. This is the coating that keeps the ink dots from spreading and reducing sharpness. Besides the obvious image resolution, receptor coatings also increase maximum black, increase color gamut, and have the ability to provide smoother tonal gradients. This is what gives inkjet prints “photo quality” . However, a down side to receptor coatings, as they are currently formulated, is that the same characteristic that attracts the subtle tiny ink droplets, also can attract contaminants in the environment, whether that be ozone from air conditioners, chemicals in heating systems of public and private buildings, fumes from urban traffic output, stong industrial floor clearners, etc. This area of study is still in it’s very beginnings and, if the media companies themselves are studying these issues at all they certainly aren’t publishing anything about it.
Spraying prints with an invisible solvent or acrylic lacquer formulated specifically for inkjet media have shown to add protection against uv light fading of the pigments, much in the way that uv museum glass does . Although these uv sprays can help to protect against some levels of moisture and atmospheric contaminants, and help from scratching prints in portfolios, these sprays are not robust enough to completely protect the media from air-borne contaminants, especially over a long period of time like months or years. So for permanent display, glass or plexi is mandatory. If you can seal the back of the frame to also help keep toxic fumes out, then so much the better.
So, from everyone I’ve discussed the issue of inkjet media permanence with, the overwhelming consensus is - if you are exhibiting your work in a public or private space for very long, make sure it is protected by having it framed behind glass or plexi. Avoid heat and problem adhesives in mounting. And, do not store your prints in any flat file or box that is made of wood or even bring them into any contact with wood products! All woods release acidic compounds and many are made with various problematic glues or stains, like in substandard portfolio boxes or mounting materials which can release fumes that can discolor prints. If exposed to wood products, putting the prints in fairly strong daylight can often reverse these yellowing effects fairly quickly, if it is done soon enough, but that is not something one wants to depend on or be faced with and the yellowing can reoccur if display or storage factors are not changed.
Anyone interested in learning more about the Aardenburg accelerated light exposure testing methods and seeing the results of his ongoing tests on a wide variety of ink/media combinations should join his website and learn how to use it. If you are a company please consider sponsoring him with a donation as a corporate sponsor. There is no better source in the world for this kind of information. This is as precise as it gets for this kind of data and we are all lucky to have it. No one else is remotely functioning on the same level.
Check it out at http://www.aardenburg-imaging.com, follow it and please donate a contribution if you like what you see.