Editor's Note: In a recent editorial in "Shutterbug" we called for information from manufacturers about the state of the art of digital imaging today, with one main topic being the longevity of "digital" prints. We are very pleased to offer this very precise and informative contribution from Dr. Nils Miller, a senior scientist with HP (Ink & Media division).

Photography is a wide-ranging field that engenders passion in its practitioners, and like all great forms of expression creates opinions formed through experience and reflection. In its early days one of the great debates was: Is Photography Art? This was the subject of many essays and heated discussions among players and spectators. Today, issues such as film vs. digital, format choices, the validity of computer generated images, photography as exploitation or revealer, and even the merits of ink jet vs. silver prints cause similar debate. We are opening this department up to readers, manufacturers, and retailers--in short, everyone who lives and breathes photography and who has an opinion about anything affecting imaging today.

Here's how to get involved: write us an e-mail at editorial@shutterbug.com or send us a letter with a proposed topic and a synopsis of your idea. Once approved, we'll ask you to send us about 500-1000 words on the subject chosen. The idea here is not to push any product or wave any flag, but to create discussion about photo and imaging topics of the day. We reserve the right to edit whatever you send in, although we will never edit intention or opinion but only for length and, hopefully, for clarity. We reserve the right to publish your work on our website as well, so you can join the archives and be a resource for opinion for years to come.

So, get thinking and writing and share your Point of View.
--George Schaub

Digital photography has dramatically changed the way we capture, store, and manipulate images. But the proof is in the print. Photo prints turn digital images into something tactile, vibrant, transportable, and physical--something you could proudly display, sell , or purchase at a high-end art gallery.

This transformation brings with it the expectation that the photo print should last for many years. Most early examples of digital photo printing technology did not live up to that expectation. Even today there are digital photo printing choices that will likely not meet longevity expectations.

There are good options for long-lasting digital prints. Following is a discussion about the general types of printing and paper technologies, and the methods by which permanence science predicts longevity for display and storage.

The Three Types Of Photo Prints
There are three primary digital printing technologies used today: ink jet, dye sublimation, and digital silver halide (e.g., lab processed). Ink jet and dye sublimation printers are the most flexible in terms of location. Ink jet printers are the most common way to produce digital photo prints.

There are two main types of ink jet ink: pigment based and dye based.

Pigment-based inks contain "particles" of colorant that, due to their relatively large size, reside on the surface of the print. Although pigment-based inks typically achieve 50 to over 100 years of display life, the tradeoff between image quality attributes (e.g., gloss, gray neutrality) and display life present a challenge for the ink designer. Photo paper choice can affect this longevity by a factor of two.

Dye-based inks contain molecular colorants that penetrate the paper surface. Early generations of ink jet dyes and even many dye-based inks available today have poor print display life--less than 10 years. Fortunately, dye chemistry advances have enabled 50 or even 100+ years of display life while still preserving the smooth surface finish and vibrant colors inherent to dyes. But this level of performance requires innovative dye-based inks (such as HP Vivera Inks) and the right "matched" paper for that particular ink.

The Two Types Of Ink Jet Paper Technologies
In general, ink jet papers fall into one of two categories. The first category is "instant dry" porous-coating photo papers (this includes "micro porous" and "nano porous"). These inorganic coatings are thick enough to absorb most or all of the ink, and do so by using extremely high surface area particles. This design spreads out the dyes over a very large surface, which makes them susceptible to fading from air pollutants such as ozone (discussed later). Pigmented inks will form pigment layers on top of these paper coatings.

The second category is papers that encapsulate ink jet dyes. For example, on HP Premium Plus Photo Paper these organic, polymeric coatings swell in thickness as they absorb the ink, and thus encapsulate and protect the dye from air fade. A subcategory might be called "partially encapsulating" uncoated papers such as watercolor papers.

Permanence Science Overview--The Four Permanence Factors
Modern permanence science must consider all key factors when determining how long a photo will last when it is either stored or displayed. Four primary factors limit the years of useful print life: Light (if displayed),Temperature, Airborne pollutants, and Humidity.

Sites for additional information on these factors include www.hp.com/go/premiumplusphoto (click on "Learn more about HP and WIR photo testing"), and www.Wilhelm-Research.com. HP and many other major manufacturers consider Wilhelm Imaging Research, Inc., as the de facto industry standard for permanencepredictions.