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A recent report from the Photo Marketing Association states, "The volume of conventional camera sales fell by nearly 17 percent in 2001.the sharp drop in conventional camera sales is due partially to displacement by digital models." As more consumers move to digital cameras, inkjet photo printing is increasing as well. This growth is a good indicator that inkjet photo prints offer photo image quality that rivals silver halide. Increasing use of digital photo and inkjet printing technologies also seems to indicate that many value the ability to create a photo that is "just right" by cropping, sizing and making other adjustments, all from the convenience of home.
Consumers also want photos that preserve the moment faithfully. They want colours to remain true, clear and vivid. For some consumers currently using or considering inkjet, this raises two questions: Are inkjet photo prints appropriate for preserving memories I intend to keep and display? Will inkjet photo prints last as long as traditional silver-halide photo prints? How long a photo print lasts depends not only on the type of print and whether it is stored or displayed, but also on the perception of the viewer. In defining perceptible or "noticeable" fade, HP considers the conservative failure criteria used by Wilhelm Imaging Research, a leading test lab, to be the most reasonable currently available.
This paper addresses photo permanence especially as it applies to inkjet photo prints. It explores the relevant environmental factors that affect photo print permanence and briefly describes how the effects of the environment can be measured. In conclusion, it discusses the display permanence of HP's current line of inks and photo papers.
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factors that affect photo print permanence |
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There are several environmental factors that can affect the permanence of photo prints. Of the two main types of photo print technologies-silver halide and inkjet ?neither technology is highly susceptible to degradation from all of these factors and none is immune to all of the factors.
light fade
Light fade is the destruction of colorants by light. Lightfastness or light fade resistance is a prediction of how long a photo print can be subjected to light before noticeable fading occurs. Light fade is often the most limiting factor associated with the useful life of displayed silver-halide and inkjet photo prints. In laboratory tests, light fade is accelerated by exposing photo prints to elevated light intensity.
dark fade
Dark fade is the relatively slow degradation of colorants caused by heat and occurs even at room temperature. Both displayed and stored silver-halide photo prints can suffer dark fade. Unlike silver-halide photo prints, there is no evidence to date that inkjet photo prints are subject to significant amounts of dark fade. Standard laboratory tests accelerate dark fade by raising temperatures and can take years to conduct.
air fade
Air fade is caused by contact with airborne gases and contaminants such as ozone. Silver-halide photo prints do not fade from contact with normal levels of gases and contaminants in air. For inkjet, the type of paper coating determines whether or not a photo print will fade when exposed to air.
Various researchers2,3,4,5 have found that coatings designed to dry to the touch immediately after printing are likely to suffer air fade. Some other types of inkjet coatings protect photo-print colorants from fade due to exposure to air. Qualitative tests of air fade susceptibility are possible, but actual quantitative predictions are not yet possible.
humidity
Because of the high levels of gelatin in silver-halide coatings, very high humidity (greater than approximately 80 percent relative humidity) encourages the growth of microorganisms that can cause discoloration. High humidity can also cause silver-halide photo prints to become "tacky." If the prints are stacked or come in contact with another surface, the coating can become damaged when pulled away. For inkjet photo prints, continuous exposure to elevated levels of humidity can cause colorants to migrate causing a shift in colour or reduced sharpness.
The industry does not currently have an accelerated method to predict humidfastness in number of years. To address the lack of a standard, HP recently developed (and plans to publish) an accelerated method to predict humidfastness. Based on this preliminary HP humidfastness test, photos printed with recently released HP photo ink and paper solutions should last for decades before unacceptable colour changes occur. Both silver halide and inkjet manufacturers recommend protecting photo prints from excessive humidity.
yellowing/staining
When chemicals or impurities in paper are exposed to light or heat, yellowing or staining can occur. Silver-halide photo prints are more susceptible than inkjet photo prints to yellowing/staining because traces of the chemicals used to develop the silver-halide image are left in the paper.
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a primer on inkjet inks and paper coatings |
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There are several inkjet photo print technologies, each offering distinctive strengths and each with different vulnerabilities to fade. The permanence of an inkjet photo print is dependent not only on the type of ink and type of paper coating, but also on the interaction of the ink and the coating.
There are two main types of inks used in inkjet photo printing: dye-based inks and pigmented inks. Dye-based is currently the most prevalent colour ink technology used in desktop photo printing partly because today's dyes offer ultimate photo image quality. Lightfastness depends on the type of dye molecule used in the ink formulation and how that molecule interacts with the paper coating in the presence of light. Pigmented inks can offer good lightfastness but not the ultimate photo image quality of dye-based inks. Therefore, in this paper, unless pigmented ink is specifically named, "ink" refers to dye-based ink.
There are also two basic types of ink-receptive coatings used in inkjet photo papers-swellable and porous.
In general, swellable coatings are comprised mainly of synthetic or natural polymers that swell when contacted with water or inks. After the ink dries, dye is left behind and encapsulated in the coating, which essentially protects the dye from any contact with airborne pollutants. See Figure 1. |
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Porous coatings for inkjet photo prints are a more recent technology designed to dry immediately after printing. These semi-rigid coatings are comprised of millions of microscopic particles. The ink flows through the spaces between the particles and deposits the dye on the surface of the particles as illustrated in Figure 2. |
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Spreading the ink exposes it to more air, which greatly shortens dry time. Unfortunately, the dye left behind when the ink dries is still exposed to air and thus is highly susceptible to fade from air pollutants. In order to protect photo prints on porous paper from air fade, the print must be displayed with protection such as glass or lamination.
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measuring and interpreting photo permanence claims |
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The science of predicting the display permanence of inkjet photo prints has been adopted from silver-halide photography. The test standard ANSI/NAPM IT9.9 1996 is often used as the test standard for inkjet photo prints as well as silver-halide photo prints. However, the ANSI standard is not an actual specification; it merely suggests test conditions and possible guidelines for predicting lightfastness. The ANSI standard's lack of specific test criteria accounts for the difference in test results from different labs. Each lab defines its own test assumptions. Among the assumptions are light intensity, type of light (e.g. incandescent bulbs, fluorescent lights and reflected or direct sunlight through windows) and the failure criteria that a user would commonly associate with noticeable fading.
Although several labs agree that the cool white fluorescent light described in the ANSI standard comes closest to real-life indoor lighting conditions, labs often differ on assumptions regarding customer-display light level and failure criteria. The lack of specific test criteria in the ANSI standard makes credible predictions complicated, but not impossible. Credible comparisons of photo permanence must be derived from identical test conditions, calculation assumptions and failure criteria.
The inkjet imaging industry is converging towards what might be called a "de facto" lightfastness test specification. Recent lightfastness claims by major inkjet print solution manufacturers refer to relatively similar test conditions and calculation assumptions.
HP and other researchers2,3,4,5 have consistently found that all porous photo papers are subject to significant air fade and swellable photo papers are not susceptible to air fade. Permanence tests show that lightfastness predictions based on standard accelerated methods (ANSI/NAPM IT9.9 1996) can be applied to the swellable inkjet photo prints without restrictions to contact with air. For the porous photo papers, the same lightfastness prediction methods can be used, but only apply when predicting fade resistance for photo prints that are continuously protected from contact with air.
In a recent lightfastness article7, Henry Wilhelm cautions that porous coated photo papers can show significant air fade if displayed without protection from air. Since many prints are displayed without protective measures, manufacturers and consumers need to be cautious about lightfastness claims for any porous coating photo paper. To avoid misleading claims about fade, HP emphasises numerical estimates of lightfastness only for swellable photo papers.
At one time, HP and others assumed that pigmented inks were not susceptible to air fade. Now there is some reason to doubt this assumption. In HP testing, a commercial pigmented ink was printed on a variety of porous papers, including two recommended by the manufacturer. Interestingly, in the initial four-month test period, measurable-but not yet noticeable-pigment air fade occurred on all samples. Until more comprehensive test results are available, HP cautions consumers making pigmented-ink photo prints to protect them from continuous contact with air to maximise display permanence.
In summary, based on the current generation of dyes/pigments and inkjet coatings, to achieve ultimate print quality and good permanence, dye-based inks on swellable photo papers offer the best solutions. How well a given dye-based/swellable solution performs depends on the specific formulations of the ink and coating and how they interact.
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HP's newest photo print solution:
fade resistance superior to silver halide |
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Early generations of inkjet photo prints had light fade resistance (lightfastness) in the range of three to ten years.8 Since most silver-halide photo print brands in Europe and the Americas have 12 to 22 years of lightfastness, early inkjet photo prints fell short. Today, claims of 10 to 25 years of "lightfastness" are routinely made for photo prints produced with branded inks, papers and printers. However, some of the papers used in these systems have porous coatings and thus show significant air fade in as little as a few weeks if displayed without protection from air.
HP's new (June 2002) photo inkjet system pushes fade resistance into a whole new realm-up to 73 years. This system combines newly formulated inks and coatings-the HP 57 tri-color print cartridge and the new HP 58 photo print cartridge on HP Premium Plus Photo Paper. This HP six-ink, fade-resistant system depends on patented ink formulations, an exclusive new dye, and a dye-encapsulating swellable paper optimised for HP dye chemistries.
The benefits derived from HP's co-developed inks and photo papers are obvious in Figure 3. |
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Photos printed with the HP 57 tri-colour print cartridge and the HP 58 photo print cartridge on the new HP Premium Plus Photo Paper even exceed the fade resistance of Fuji Crystal Archive, the most fade resistant silver-halide paper.7 Using just the HP 57 tri-colour print cartridge with the HP Premium Plus Photo Paper, for three-ink photo printing, still delivers fade resistance consistent with silver halide. However, substituting a competitive photo paper in this solution is likely to significantly reduce fade resistance. This is true for all the non-HP papers HP has tested.
Digital photo enthusiasts will find the HP 57 tri-colour print cartridge, HP 58 photo print cartridge and HP Premium Plus Photo Paper system available on several different HP inkjet printers introduced this summer and more in the future. These printers offer a variety of feature choices across a range of price points. The HP 58 photo print cartridge will come with newly introduced HP photo printers and will be available for purchase for optional use on several other HP printers.
The HP 57 tri-colour print cartridge and HP 58 photo print cartridge in combination with HP Premium Plus Photo Paper form a system that offers true-to-life, virtually grain-free photo prints that resist fading for generations-with all of the flexibility of digital photography.
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summary |
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The science of estimating photo permanence has matured and evolved with the growing importance of inkjet photo prints. The industry appears to be moving toward a more specific lightfastness standard, which will benefit comparisons of all photo print technologies in the future. HP has applied, and, where necessary, developed tests for other permanence factors to help ensure the overall permanence of HP inkjet photo prints.
The fade resistance of HP's latest generation of inkjet photo prints can be credibly compared to silver-halide photo prints. And, one HP ink and photo paper system even surpasses the fade resistance of all silver-halide photo paper. With HP's latest generation of six-ink photo prints, consumers can feel confident that their prints offer excellent resistance to environmental factors that degrade photos and that displayed photos will resist fading for generations.
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Nils Miller serves as the technical liaison between HP's inkjet ink and media research and development organizations. He is a key technical leader on strategic development projects and manages HP-sponsored ink and media research programs at several universities and institutes. Miller has a B.S. in chemical engineering from Oregon State University and aPh.D. in chemical engineering/physical chemistry from the University of Washington.
For more greater depth on the subject of photo permanence and for more details about the HP test results discussed in this paper, see the Nils Miller paper "Inkjet Photo Prints: Here to Stay" published by HP in June 2002.
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Glossary |
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Air fade - Degradation in an inkjet image that is caused by contact with airborne gases and contaminants
ANSI/NAPM IT9.9 1996 standard - Standard which deals with measuring the image stability of colour photographic materials; divided into two parts with first covering the methods and procedures for predicting the long-term, dark storage stability of colour photographic images; second part covers the methods and procedures for measuring the colour stability of such images when exposed to light of specified intensities and spectral distribution at specified temperature and relative humidities. ANSI: American National Standard Institute NAPM: National Association of Photographic Manufactures
Colorant - Substance for colouring a material; can be dye or pigment
Dark fade - Thermal degradation of an image in the absence of light
Dye-based ink - Ink containing dissolved colorants in molecular form
Fade - Destruction of the colour-generating characteristics of colorants
Humidfastness - Migration of colorant when a photo image is exposed to elevated levels of humidity
Inkjet - Printer technology in which droplets of ink are projected onto paper
Lightfastness - Prediction of how long a photo image can be subjected to light before noticeable fade occurs (also called light fade resistance)
Ozone - Colourless gas that is naturally formed in the atmosphere by a photochemical reaction; a major air pollutant in the lower atmosphere but a beneficial component of the upper atmosphere
Pigmented ink - Ink containing insoluble colorant particles
Silver halide - Photofinishing technology that uses light to expose an image onto the silver-halide crystals in photo paper; the image is developed when it comes in contact with chemicals that activate dyes that are also a part of the photo paper
Staining - Discoloration due to degradation of residual chemicals or other impurities in photo paper (also called yellowing)
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1Photo Marketing Association, Photo Industry 2002: Review and Forecast, 2001:3.
2M.D. Stone, PC Magazine, January 16, 2001:52.
3M. Oakland, D. Bugner, R. Levesque and R. Vanhanehem, Proceedings of IS&T NIP17: International Conference on Digital Printing Technologies, October 2001:175-178.
4D. Sid, Proceedings of IS&T NIP17: International Conference on Digital Printing Technologies, October 2001:171-174.
5H. Onishi, M. Hanmura, H. Kanada and T. Kaieda, Proceedings of IS&T NIP17: International Conference on Digital Printing Technologies, October 2001:192-196.
6ANSI (American National Standards Institute), NAPM (National Association of Photographic Manufacturers). For more details, please see the Glossary at the end of the document.
7Henry Wilhelm, "How Long Will They Last? An Overview of the Light-Fading Stability of Inkjet Prints and Traditional Color Photographs," IS&T 12th International Symposium on Photofinishing Technology Proceedings book, 2002:32-37.
8Based on de-facto standard assumptions or Wilhelm Imaging Research assumptions, which are similar. |
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