The issue of print permanence is an old one and a great deal of research has been done on printing technologies, all the way from silver-halide films and papers through to the latest inkjet and dye-sublimation media.

Making Your Prints Last

The issue of print permanence is an old one and a great deal of research has been done on printing technologies, all the way from silver-halide films and papers through to the latest inkjet and dye-sublimation media. The leading research organisation is Wilhelm Imaging Research (www.wilhelm-research.com), which is totally independent of any media manufacturer. Run by Henry Wilhelm, who has been involved in image-preservation research since 1965, WIR uses test procedures developed by the American National Standards Institute and ISO.

Photographic and digital print materials are tested by accelerated aging, which involves exposing prints to standardised light levels under controlled conditions that replicate typical display and storage situations. From these tests, estimates of probable light-fast times result and these are used by many printer and media manufacturers.

Some manufacturers also conduct their own light-fastness tests. However, be wary when looking at their results as these tests often differ quite substantially from Wilhelm’s standard procedures so comparison with Wilhelm’s published results for particular products are not necessarily valid.

Identifying Changes
How can you tell when your photographic images have begun to deteriorate? Without scientific testing conditions it’s impossible to identify the point at which fading and colour changes occur. By the time these changes are visible, some of the original ‘quality’ of the picture is lost.

Some features to look for include:
1. An overall loss of colour density and contrast (the picture loses its original ‘zap’);
2. Shifts in the colour balance that occur because the dyes that make up the image fade at different rates;
3. Loss of image detail and sharpness;
4. Overall yellowing of prints;
5. Surfaces of prints may also be damaged physically, by abrasion, cracking, de-lamination or fingerprints or through attacks by fungi or other micro-organisms.

Fortunately, as long as the deterioration is relatively minor, many photographs can be ‘restored’ to resemble their original conditions by software that is applied as part of the scanning or copying process. Most scanners include this software.

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An example of the fading and loss of detail and colour saturation that can occur over decades. The original image was shot on slide film, which accounts for its relatively high contrast.

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This silver halide B&W print has yellowed over about half a century due to chemical changes in the emulsion.

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An inkjet print whose surface has been damaged by abrasion. Pigment prints on textured papers are more susceptible to surface damage than dye prints on glossy papers.

What Causes Prints to Change?

Whereas traditional photographic media were mainly affected by light exposure and their dyes generally faded at a fairly uniform rate, digital printing materials are influenced by a much wider range of factors, including:
* The nature of the paper itself, the inks used and the combination of ink with paper.
* Environmental conditions covering light, heat, humidity, atmospheric contaminants and handling.
* Display and/or storage conditions.

These factors may combine, making it complicated to tease out which of them are responsible for the colour changes. If you understand how they work, you can adopt strategies to reduce most of the above-listed effects and maximise the chances that your digital prints will remain colourful and attractive. Consequently, we will look at each of these factors in turn.

Media: There is no ‘one-size-fits-all’ solution if you want long-lasting inkjet prints because best results are obtained from certain ink/paper combinations. A printer that produces long-lasting prints on one paper may not deliver the prints with the same stability when a different brand of paper is used – even though the two papers look almost identical.

Photo inkjet papers use either ‘swellable’ or ‘microporous’ coatings. On swellable papers, the coating contains a polymer that swells as it absorbs the ink. A hardening agent is added to strengthen the coating as the polymer dries. Drying can take several minutes and prints are easily smudged during this time. Swellable papers are more colour-stable because the coating swells up to enclose the ink, protecting it from environmental contaminants. However, swellable papers are sensitive to high humidity.

The surface of microporous papers is coated with millions of tiny particles in a quick-drying binder. These particles form a structure with many tiny spaces, creating a large area that absorbs ink. Spaces at the surface allow the ink to penetrate quickly and the pores absorb the ink by capillary action. The large surface area of microporous papers allows it to dry very quickly. The faster the paper dries, the faster you can print and the lower the chance of smudging as the paper exits the printer.

The small particles in microporous coatings reflect more light, making colours brighter. The ink also spreads less, so prints look sharper than on other surfaces. However, the open areas of the coating allow the ink to come into contact with atmospheric contaminants. Microporous papers are easily identified: if it squeaks or ‘grabs’ when you run your finger across the paper, it’s probably microporous. (Most glossy inkjet papers are microporous.)

High quality, acid-free papers have greater inherent stability than standard papers, which is why they are used for all archiving and fine-art applications and most traditional photography. As we explained in Chapter 4, pigment inks are generally more fade-resistant than dye-based inks, although some recent dye inks have lightfastness ratings of 100 years or more. But even the latest dye inks can have stability problems on some ‘fine-art’ papers.

The resolution setting you use for printing can also influence the stability of your prints – although not to a large degree. So can the ways in which dye inks combine. A cyan ink, for example, may be very stable in a cyan patch, but fade rapidly when mixed with magenta to make blue.

Short-Term Colour Changes

When dye inks are absorbed into the upper layer of the printing paper, both physical and chemical changes occur as the colour is locked into the paper surface. These changes, which are more prevalent with microporous papers than other types, may produce short-term colour shifts that can persist for minutes, hours or even days after the print is produced.

Short-term colour changes can be annoying for digital photo printers because it’s difficult to predict how long it will take for the colours to stabilise. Consequently, you cannot know the print is colour accurate for up to 24 hours after the original test print was made. For professional photographers, post-production colour instability is a disaster area. Not only does it make production workflows inefficient (because you have to wait for colours to stabilise before making a final print); it can also be difficult to colour-match reprints when clients request them.

Environmental factors: The environments in which prints are displayed and stored can also affect print stability. However, teasing out which factor is responsible for a particular type of degradation can be difficult. Most commonly, colours change as a result of chemical changes in the dyes that make up the image, leading to a loss of colour (fading) or a change in the dye chemistry (normally due to oxidation) that causes a shift in colour balance.

The effects are often different on different ink/media combinations and with different colours. Light can cause differential fading in inkjet prints, with magenta dyes being the most susceptible to change. Cyan dyes, on the other hand, are most susceptible to chemical contaminants and, as they fade, prints can turn orange in a short time.

Many paper/ink combinations are highly sensitive to ozone, which is common at low-levels in urban environments (and at relatively high concentrations around electrical/electronic items such as refrigerators and air conditioners). Research has shown that more than 40% of all photographs displayed in a typical home have been put up on the refrigerator door – usually without protection.

Fading is also faster in polluted urban environments (especially in smoke-filled rooms) than in rural areas and faster in humid cities like Cairns than in arid cities like Alice Springs.

Printing procedures: As a rule, the highest durability and best image quality are achieved by printing with the papers and inks recommended by the printer manufacturer. But the way prints are stored and displayed can affect their durability. To obtain the maximum stability from your inkjet prints it is best to allow for a period of ‘curing’ while the inks stabilise.

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The lower picture shows what can happen when a dye-ink print on microporous paper is posted on a refrigerator door for approximately six months. The picture above shows the colours in the original digital image file.

We recommend covering each print with a sheet of plain paper as it comes off the printer (after allowing a minute or so for it to dry) and then leaving the covered print for at least 24 hours before mounting it for display or storing it in an album or box.

Display and storage: Encapsulating inkjet prints in plastic (‘laminating’) is a cheap and effective way to protect them against atmospheric pollutants. It’s also a good way to protect traditional photo prints against dust, moisture and airborne fungal spores. Prints that have been stuck on a refrigerator door or pinned to a cork board are vulnerable to all these contaminants, although when certain combinations of inks and papers are used, lightfastness ratings for unprotected prints can exceed 75 years.

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Framing prints protects them against atmospheric contaminants.

Framing inkjet prints behind glass is an excellent strategy for pictures you want to display. Make sure the backing and matt you use are acid- and lignin-free and seal the frame with tape to prevent dust, moisture and insects from getting in and damaging your print. Avoid displaying photo prints in strong, direct sunlight as it can cause differential fading in inkjet prints, with magenta dyes being the most susceptible to change.

Lightfastness Data

Wilhelm Imaging Research (www.wilhelm-research.com) publishes the results of its tests on inkjet printers whenever new models are released, allowing prospective buyers to view lightfastness ratings with a range of media. The company also conducts regular tests of photolab printing systems and ‘third-party’ inks and papers.

hotographers with collections of silver halide prints, films and slides can also learn about the potential lifetimes of a range of media and the best ways to preserve their pictures by reading Wilhelm’s 758-page book, The Permanence and Care of Color Photographs, which is available in PDF format as a free download from the site.

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