What you should know when choosing media and service providers for printing your photos.

This article looks at the factors that affect print durability and how long you should expect prints to keep their colours and contrast in different conditions. We also outline the methods used to provide reliable information on print durability and the factors that can cause prints to fade.

This pair of images illustrates the effects of prolonged light exposure and the presence of atmospheric pollutants, particularly ozone, on the dyes used in traditional silver halide and dye-based inkjet prints. The upper image represents the original snapshot, while the lower one shows the kind of fading that can occur when a print made in a traditional photolab is displayed on a fridge door for a few months – or years, depending on the media used to print it. Fading would normally be slower in prints made with the latest, more durable dye-based inks.

Testing durability

Two organisations routinely test printing media for various parameters, concentrating mainly on resistance to fading under prolonged light exposure in conditions that simulate normal home and office environments. They also test for dark stability (storage without light exposure) and resistance to ozone, a powerful oxidising agent often found around appliances like fridges.

Wilhelm Imaging Research has been running comprehensive tests since 1971 and covering both traditional and digital inks plus a wide range of printing papers.  The tests provide light fastness ratings based on exposures at 450 lux for 12 hours per day, with results estimating the time necessary to reach ‘noticeable’ fading at 24oC and 60% humidity. A 25MB ‘reference collection’ is available from the site as a free download with test data from 1971 to 2018.

Aardenburg Imaging and Archives, founded in 2007 by Mark McCormick-Goodhart, provides a more up-to-date resource on printmaking and image permanence for members (membership is free). Its tests are slightly different from the tests by Wilhelm Imaging Research. They provide data in Megalux hours of cumulative exposure with upper and lower limits for different light levels. Aardenburg also offers information on Light Induced Low-Intensity Staining (LILIS), a new issue caused by complex chemical interactions between Titanium Dioxide (TiO2) and Optical Brightening Agents (OBAs), which are common in RC (resin-coated) media.

Unfortunately, both companies struggle to keep pace with new products as they are released. The best you can hope is to search using the name of a particular ink set or paper brand/surface. 

Traditional processes

Traditional silver halide-based printing processes generate the image with chemical dyes, which can be quite vulnerable to light fading. Both prolonged light exposure and exposure to atmospheric pollutants, particularly ozone, can break chemical bonds, causing colours to change. Gelatin emulsions can also absorb moisture from the air and will become sticky under high humidity, which makes prints vulnerable to fungal infections. Most 20-year-old prints will show impacts from long-term display and/or storage.

In addition, traditional media are not particularly environmentally friendly. Although most photolabs have procedures for handling and disposing of waste, it’s expensive and many local councils and shopping centres don’t want chemistry going down their drains.

Providing power to processing equipment is also costly since it must be kept running continuously, even when print volumes are low. Heating is needed in winter and air conditioning in summer.

All these factors mean traditional printing is rapidly being replaced by ‘dry’ digital printing, which has the combined advantages of non-polluting materials, low power costs and the ability to be operated on an as-needed basis at ‘normal’ temperatures and humidity levels.

Digital printing

Inkjet is the most common technology used for digital printing by both consumers and businesses, with two types of media: dye-based and pigment-based. Most consumer-level and business colour printers use dye-based inks, while most professional printers use pigment inks.

This diagram shows the basic difference between dye and pigment inks.

Dye and pigment inks have different vulnerabilities. Because they are absorbed into the surface coating, dye inks are more susceptible to light and chemical degradation. Pigment inks, which sit on the surface of the paper, are more vulnerable to abrasion.

Although many inkjet papers are labelled as suitable for dye or pigment inks, in reality each ink type will perform better with a specific range of surface coatings. For dye inks, the coating must absorb the inks, which is why they tend to produce better results with glossy, lustre and semi-gloss papers. For pigment inks a slightly roughened surface is needed to trap the ink particles, hence their suitability for matte and ‘fine art’ papers with smooth or textured surfaces.

Durability comparisons

Because both use chemical dyes, the lightfastness of inkjet dye media is similar to that of the best silver halide media.  Pigment inks are usually more resistant to light-induced fading. The illustration below compares results from typical media in the three categories.

But it doesn’t stop at the different ink sets; different papers will respond differently to a particular ink set. So, when checking lightfastness ratings you must take account of both the ink set and the paper on which the print is made.

The tables below give Aardenburg’s Conservation Display ratings for two Canon ink sets, one dye and one pigment. A second set of  tables illustrates the differences between a dye ink set and a pigment ink set with two Canon printers.

Paper Rating
Canon Photo Paper Pro Luster LU-101 11-33 Megalux hrs (LILIS)
Canon Photo Paper Pro Platinum PT-101 22-28 Megalux hours
Canon Photo Paper Plus Glossy II PP-101 23-48 Megalux hours
Canon Photo Paper Plus Semi-Gloss SG-201 55 Megalux hours
Epson Proofing Paper White Semimatte 28-40 Megalux hours

This table compares Canon’s ChromaLife 100+ dye inks used in its Pixma Pro-100 printer across four different papers from Canon’s range plus Epson Proofing Paper White Semimatte.

Canon Heavyweight Satin Photographic Paper 300gsm 104-134 Megalux hours
Innova F-Type Gloss Warm Tone 300gsm 76-85 Megalux hours
Hahnemuhle FineArt Pearl 285gsm 81-93 Megalux hours
Hahnemuhle Photo Rag Baryta 315gsm 86-106 Megalux hours
Ilford Galerie Gold Fibre Silk 97-114 Megalux hours
Epson Exhibition Fiber 325gsm 37-80 Megalux hours

This table shows Canon’s Lucia pigment inks used in a Canon iPF5000 professional printer with a variety of papers from different manufacturers.

Aardenburg’s tests have identified another factor that can affect print durability: Light Induced Low-Intensity Staining (LILIS). This measures the yellowing that occurs in real world storage and display conditions and is caused by complex chemical interactions between Titanium Dioxide (TiO2) and Optical Brighteners (OBAs) in papers.

Photo Review published an article on optical brighteners before the Aardenburg results were released. It’s worth checking out because we’ve included a list of popular inkjet papers separated into three groups: those we know include OBAs, those that definitely don’t and those for which the presence of OBAs is not specified.

Commercial printing technologies

Alternative printing technologies include dye sublimation and thermal offset printing. In the former, images are produced by dye diffusing into an image receiving layer on the paper. It’s found in photo booths and snapshot printers that use combined ink-plus-paper cartridges.

Thermal offset printing is only used by commercial machines like the HP Indigo printer. The ‘inks’ consist of resin-encapsulated pigments dispersed in a volatile liquid. They are deposited by thermal offset, which bonds a very thin layer of ink to the surface of the paper.

A wide range of pigments can be used in thermal offset printers, enabling them to cover up to 97% of the PANTONE colour gamut, which is similar to professional inkjet printers. Lightfastness tests show high stability for the cyan inks, marginally lower for the black inks, a little less for the magenta ink and moderate stability for the yellow ink. This means prints can suffer from colour shifts over time.

Durability ratings are similar for Fujicolor Crystal Archive paper, the most durable of the silver halide media. Wilhelm Imaging Research gives it a lightfastness rating of 60 years before noticeable fading occurs, while Aardenburg ‘s tests showed fading could become noticeable after 30 Megalux hours (million hours at one lux) of light exposure.

This graphic shows the results of tests by Aardenburg Imaging and Archives on dye and pigment inks on three different paper types, compared with the highest-durability traditional silver halide media.

So-called ‘dry’ minilabs normally use inkjet technology, in most cases with dye inks. The Noritsu machines use four colours: cyan, magenta, yellow and black (CMYK), while the Epson SureLab machines add light magenta and light cyan to the basic four-colour ink set.

According to Keith Cooper at Northlight Images, who tested the Epson SureLab SL-D700 in August 2018, print longevity from the Epson machines should be on a par with the similar ‘Claria’ inks used in desktop and wide format photographic printers. However, Cooper’s tests showed B&W prints were affected by metamerism (where colours look different under different types of lighting), with a print showing a slight brown/magenta cast under halogen lighting and taking on a slight greenish look in diffuse daylight.

Other factors

According to Aardenburg, the other factors that can affect print durability include fading and/or staining caused by heat, humidity and air pollutants. Mould damage can also occur at high humidity. Also, temperature and especially humidity cycling can cause physical cracks and/or flaking, etc.

Handling damage such as scratching, abrasion, tears and creases and catastrophic damage by smoke, fire, floods, etc., can also degrade print quality over time. Aardenburg also notes that as illumination levels where images are displayed are reduced, other forms of degradation will take on a greater proportion of risk and may appear in shorter time intervals since UV radiation can slow fungal growth.

Reproducing colour gamut

Many screen display devices can display a much wider gamut that even the best printers can reproduce, largely because they have a wider brightness range. Today’s inkjet printers strive to reproduce a gamut that is as close as possible to the screen displays, although prints on paper can never match them. By default, all digital minilabs and home photo printers are set intentionally for the sRGB working space, which is also the default setting for most cameras.

This diagram plots the colour gamut of a typical modern ‘dry’ lab against the plots of an older digital printing press and traditional silver halide media. It shows modern digital printers can reproduce a wider range of colours than either older printers or traditional phootlabs.

The technology used by the printer also influences the colour gamut in the print. Traditional pigment-based inks tend to have a lower gamut than dye-based inks, so more individual colour inks are required to attempt to cover the same or a similar colour gamut.

Commercial printers usually include auto enhancement algorithms that adjust sRGB images so they print with ‘pleasing’ colours and tones. Some ‘dry’ labs can reach up to 97% of the PANTONE colour gamut, which represents all the colours that can be reproduced by printing presses.

Large format (A3+ to A2) desktop printers with six or more inks can usually match the gamut of the best dry labs and will often exceed it.  Printing your photos at home gives you personal control of both the software interface and all the menu settings and advanced users can take advantage of ICC profiles to ensure colour accuracy and manually tweak tone and colour values for added creativity.

Article by Margaret Brown (see Margaret’s photography pocket guides)

Excerpt from Photo Review Issue 84

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