A Visual Survey of Colour on Paper and Colour Changes During Exposure to Light

This paper presents how inkjet colour is affected by firstly the substrate and secondly exposure to light and the combination of both. The research uses both pigmented and dye based inks printed onto coated and uncoated fine art papers, and are subjected to light conditions that are constantly changing through out the day and consequently the year. Although benchmark conditions and standards as issued by Wilhelm Imaging Research (1) are useful, once a printed artwork enters the public domain artworks may be subjected to conditions beyond expectations of the laboratory, such as changes in light, humidity and pollutants. Colour patches were printed onto a variety of artist’s coated and uncoated papers and then measured and photographed. The microphotography shows how ink sits within the fibres of the paper, and how colour and colour combinations changes over time. Introduction Inkjet technology has enabled the artist to print high quality photographic images; and through the use of wide format printing the potential for large-scale artworks has expanded creative vision. Similarly the ability to print, for example, banner sized works has also enabled a more professional means of presentation for exhibitions and display. Furthermore with this increase in scale artists are able to move beyond the frame. However to execute the work successfully the artist requires a range of suitable paper, both of surface quality and weight, accurate colour and tonal range, and colour that is consistent and conservable. There is a requirement at this point to make a distinction as to the expectation of longevity for printed artworks. Fine art original prints require more colour permanence and subjective surface quality than for example an exhibition display, which is more than likely only required for the lifetime of the conference or exhibition. There is an imperative by artists to produce works that do not damage their reputation, both in terms of image quality and permanence. There should also be considered the museum ‘old master’ reproduction, for which there is an expectation by the buyer of a degree of colour fastness or permanence. Early tests (2) made at the CFPR showed that some prints might show some shift in colour and fading beyond acceptable levels as early as a few months. Subsequent tests have revealed that through a combination of appropriate substrates, colour profiling (3) and pigmented or UV based inks the longevity of printed works can be greatly increased. In December 2001 a project was implemented with Hewlett Packard, through their Art and Science funding programme to produce the First International Digital Miniature Print Portfolio (4). In order to ensure the digital prints were printed using the best inks and were compatible with the paper stock, we initially undertook an accelerated exposure on a small range of uncoated and coated papers. Whilst the accelerated tests indicated pigmented inks were more stable on enhanced papers than dye based inks, we wanted to look at the relationship between paper and ink, to obtain a better understanding as to how ink faded, and to undertake a record of fading characteristics. Real time testing obviously requires a long-term approach to a project. In March 2002, a second series of lightfast tests on a range of papers commenced, followed by a more detailed investigation in December 2002, which involved the use of colour measurements and the documenting of the surface of the paper through microphotography. An analysis of paper A necessary aspect of this research is the substrate and an evaluation as to the relation of ink and paper, surface quality of the paper and the surface quality of ink on paper. Printmakers using traditional print processes, in general, are used to handling and printing onto quality fine art papers. Some papers are suitable for a particular process and have certain characteristics, for example, the way it is manufactured or the fibre content. For traditional printmaking, the artist has a wide variety of papers from which to choose. When inkjet printing the artist has a more reduced range of papers available. This is not to say that papers specially designed for inkjet are unsuitable; however there are subjective criteria for the artist, such as paper colour, weight and surface, which is both important to the artist and the impact of the image. Although a bright, white, smooth, gloss or matt finish, offer the optimum conditions for saturation of colour and colour reflectance, this is not necessarily the requirement for the artist. Whilst users who require a high turnover print production require a consistency of image, this does not necessarily mean that the image has a high subjective visual quality. By quality we mean, colour resolution, parity to the image on the screen, contrast, colour range, subtlety of tone, continuous tone, good light tone, how it interacts with the paper. An initial evaluation of 66 fine art printmaking papers was undertaken. The papers ranged from lightweight Japanese tissues to heavyweight etching papers (5). There was also a variation in the base colour of the paper, which ranged from a bright white to an antique cream. A print containing a photographic image, fonts in varying sizes, and CMYKRGB colour patches were printed onto the paper samples. The selection of papers was not necessarily based on colour fidelity (6), especially as there was no original to compare. In fact papers that showed brightly printed results were not necessarily chosen. Papers were chosen for qualities relating to surface texture, ink capacity and the ability to hold detail without feathering; and lastly a paper that could have the potential for further development such as ICC profiling. Around 15 papers were chosen and included Japanese papers and samples from the Somerset, Arches and Fabriano mills, which are further being trialed in combination with enhanced papers for lightfast testing; and in collaboration with the UK’s primary paper merchant for fine art papers to write colour profiles. Lightfast colour Lightfast tests were undertaken using dye and pigmented inks onto artist’s cotton based handmade, uncoated and coated inkjet papers. Thirty-seven papers were tested, including six coated papers some of the more popular artists’ printmaking papers to which an ink receptive layer is added. The printed tests were exposed to light conditions that simulated a gallery or home environment around 300 – 600 lux. Colour samples containing Cyan, Magenta, Yellow, Black and CMY patches at 5% increments were printed using Hewlett Packard UV (pigment) inks and dye-based inks on a 42” HP5000ps. After 11 months, measurements were made on patches containing 50% ink coverage. These patches were then measured using a Gretag Macbeth spectrophotometer using an illumination D50 and at an observer angle of 2 ̊, so that colour patches are accurately measured and compared. Colour patches were also photographed using a SP-200xm metallurgical microscope that has a reflective light source, designed for non-transparent samples. The microscope light source illuminates the surface of the sample from above. Colour patches were photographed under x4 and x10 magnification using a Canon G3 digital camera. The images were converted to Tiff files and saved with no compression to ensure accurate repeatable colour data. Cyan, magenta, yellow, red, green, blue, black colour patches at 50% ink levels and a composite black patch at 100% were photographed. These samples will be photographed again at regular intervals through out the year(s). Tests begun in March 2002 Delta E differences were recorded between recently printed samples (reference data) and exposed samples (measured data). Delta E averages are calculated here showing the average difference in fading rates between CMYK, uncoated and coated, dye and pigment. Average ΔE differences after 11 months: Dye Cyan Magenta Yellow Black Coated 19.8 66.45 25.3 39.7 Uncoated 3.59 21.51 21.86 16.02 Pigment Cyan Magenta Yellow Black Coated 10.4 10.4 5.7 6.66 Uncoated 10.7 9.82 5.71 5.51 The results suggest when printed on coated papers the magenta in the dye samples appears to be particularly fugitive, resulting over time, in a greenish blue cast to the prints. Similarly for the uncoated papers the cyan is resistant to fading and therefore creates a similar greenish-blue result. However for pigmented inks the fading rate appears to be more consistent for both enhanced and uncoated papers, with yellow and black being the least resistant to fading. Tests begun in December 2002 For the subsequent colour trial printed samples include cyan, magenta, yellow, black, composite black and red, green and blue patches. Average ΔE differences after 3 months: Dye Cyan Magenta Yellow Black Coated 9.74 11.84 10.16 0.48 Uncoated 1.72 4.33 1.33 0.62 Pigment Cyan Magenta Yellow Black Coated 0.7 2.02 1.23 0.55 Uncoated 0.9 1.86 1.04 1.14 Results after three months show fading of dye based inks on coated papers only with an average of 8.05 ΔE, which drops considerably to a 2ΔE with dye inks printed onto uncoated papers. However for pigmented inks on coated papers the average ΔE is around 1.12 and an average of 1.23 for pigment based inks on uncoated papers. The slight rise for coated papers might indicate anomalies that arose such as darkening of Japanese papers and potential chemical reactions occurring with differing manufacturing processes. Photographing the samples Colour patches on paper samples were photographed at 50% ink coverage. The colour patches photographed were cyan, magenta, yellow, red, green, blue, and black at 50% and 100%. Fig.1 50% cyan pigment on coated 50% cyan pigment on uncoated 50% cyan dye on coated 50% cyan dye on uncoated Dye and pigment based samples printed onto coated and uncoated papers revealed two differences: the surface structure of the coated an uncoated papers and the intensity of the cyan. Examples here (fig.1) show pigmented inks printed onto coated and uncoated paper. Although printed using the same hardware and inks, the HP5000ps also prints a light cyan and light magenta ink. There is a discernable difference between the rounded regular dot structure on (fig.1) the coated (TLHC) and a more crystalline structure of the uncoated (TRHC) where the ink has been absorbed into the paper fibres. This is all the more exaggerated in for example a Japanese Rayon paper (fig.2), which has a much looser weave, and which illustrates the network of fibres and how the ink is encapsulated within the fibres. Fig.2 50% cyan on Rayon 50% composite black on Rayon Papers that are coated or infused (7) have a receiver layer that holds the ink droplets close to the surface, the surface of the paper is generally smoother and much brighter, and reflects colour more successfully than uncoated papers. For an uncoated paper the fibres are still visible and the ink falls within the peaks and troughs of the fibres, the colour is reflected in different directions therefore making the image duller and flat. This can be also compared in the microphotographs where the light shone onto the coated samples is displaced evenly, whereas the light source falls unevenly onto the uncoated paper samples, making some areas ‘glow’ and some areas appear dark. Uncoated papers are also more difficult to photograph, due to the level of magnification and depth of field; some areas are therefore out of focus. Photographing Colour Changes The photographs taken at the beginning of the test period, and subsequent photographs made of samples that have had 11 months of exposure, illustrate which colour has a tendency to fade. An initial visual difference between the dye and pigmented inks is the colour content of the cyan, which has a significant effect on colour balance and fading results for the dye-based inks. For pigmented inks black and yellow are the most resistant to fading. After 11 months (fig. 3) the dye coated paper sample (BRHC) is paler. Here the dots have receded in size and are wider apart and the light cyan dots have faded from the paper. The dye on the uncoated sample (BRHC) has faded consistently with the pigment on uncoated sample (TRHC). In general, both samples on uncoated (fig. 4) show there is no defined dot, which is more irregular; the ink has taken-on the character of the paper fibres; there is no distinction between cyan and light cyan; and the pigment sample (TRHC) appears paler, although there is less fading. Fig.3 Samples photographed after 11 months 50% cyan pigment on coated 50% cyan pigment on uncoated 50% cyan dye on coated 50% cyan dye on uncoated For composite cmy samples, similar characteristics can be observed in as much that the dots have receded in size and grown wider apart, light cyan and light magenta dots have faded and the magenta has near completely faded; and through secondary colour mixing of the cyan and yellow has resulted in an olive brown colour. Other composite samples such as red (Magenta + Yellow) indicates early colour shift in the dye sample as early as 2 months (fig.4). Other indications that affect colour changes Colour measuring has also highlighted colour differences in which the sample has darkened. Subsequent measuring of the paper (8) has indicated that Japanese samples, indicate a darkening or yellowing, suggesting that the fibre content can contribute to colour difference. Many of the accelerated lightfast tests yellowed the surface of coated papers, although this has not occurred during any real–time tests. There was an assumption that ink on papers made by the same manufacturer would fade at the same rate. This has not been the case. Different manufacturing processes, such as the texture, sizing and construction of the paper can contribute to or inhibit the fading process. Another suggestion is the chemical effect of one colour on another. When printed separately a colour retains fidelity, however when combined with another is weakened and becomes more fugitive (9). Fig.4 Samples photographed after 11 months 50% red pigment on coated 50% red pigment on uncoated 50% red dye on coated 50% red dye on uncoated Future objectivesThrough a government led sponsored project into writing colour profiles for fine artpapers, the next objective is to photograph and expose paper samples that are printedwith appropriate colour profiles. The profiling enables the correct percentage of ink tobe printed and therefore increases ink levels and colour saturation.A second objective is to use bespoke ink sets, which would include white and ortransparent colours. References(1) http://www.wilhelm-research.com(2) Parraman. C. 2001 The Impact of Paper on Ink: From the PhotomechanicalPrinter’s Perspective, IS&T;/SID Ninth Color Imaging Conference, Arizona, USA,Nov 6-9 2001, p.217(3) Wang.H. 2003 The Application of Colour Management System to Improve theQuality of Ink Jet Printing on Fine Art Paper, Preservation and Conservation Issues Related to Digital Printing, The Physics Congress, 23-27 March Heriot-WattCampus, Edinburgh(4) http://www.uwe.ac.uk/amd/cfpr/(5) A Useful description of artist’s papers can be found in: Turner, S. Which Paper? A Review of Fine Papers for Artists, Craftspeople and Designers, Estamp London(1991)(6) Farnand, S. Using ΔE Metrics for Measuring Color Difference in Hard-CopyPictorial Images, 15th Electronic Imaging Santa Clara, California, 20-24th January2003(7) The site http://www.mwords.co.uk/pages/FAQ/articlePaperTypes.htm gives auseful outline on methods of coating papers.(8) Papanagiotou, C. 2000 An Investigation of the use of digital colour matching forthe toning of papers using ink-jet printing, The Paper Conservator, vol 20,p73 (9) Bugner, D.E. Comparison of Image Stability of Digital Photographic PrintsProduced by Various Desktop Output Technologies