How Many Inks? The simplest printers use four ink colours: cyan, magenta, yellow and black. Such printers are commonly known as CMYK printers, the ‘K” standing for ‘key’ and representing black. In theory, all other colours can be produced by combining these four colours in different proportions. However, it is almost impossible to produce inks that are totally colour-pure so printer manufacturers have developed ink sets with increased colour and tonal accuracy.
1. How Many Inks?
The simplest printers use four ink colours: cyan, magenta, yellow and black. Such printers are commonly known as CMYK printers, the ‘K” standing for ‘key’ and representing black. In theory, all other colours can be produced by combining these four colours in different proportions. However, it is almost impossible to produce inks that are totally colour-pure so printer manufacturers have developed ink sets with increased colour and tonal accuracy.
The first big step was to add light cyan and light magenta inks to the basic set. Subsequent additions have included green, red and blue inks, all of which increase the hue and tonal subtleties the printer can produce, yielding even better prints. Black & white printing has also become greatly improved by the addition of mid-grey and light grey inks, which fill in the deficiencies of the standard ink sets.
The essential message is that the more inks a printer can use, the greater the subtlety of tonal nuance it is capable of – and the better the end result. The real differences show up with enlargements at A3 size and over, especially in portraits. More information on this topic can be found in Choosing Software and Printing Raw Files.
The classic CMYK ink set.
The addition of light cyan and magenta inks plus mid and light grey and separate black inks for glossy and matte papers creates and ink set for professional-quality photo printing.
2. What Type of Ink?
Selecting an inkjet printer usually locks you into a particular ink set, which may be formulated from dye-based or pigment-based colours. Dye-based inks consist of liquid colourants that have been dissolved in a fluid vehicle. They are readily absorbed into the top layer of the printing paper and can be deposited quickly in extremely tiny drops.
Pigment inks consist of minute particles of insoluble colours, which some manufacturers enclose in an impervious resin coating. Both types of inks can be laid down in extremely tiny droplets, producing prints with fine tonal gradations. Droplet sizes of 1.5 to 2 picolitres (two trillionths of a litre) are common among photo printers.
Epson’s Variable-sized Droplet Technology allows the size of ink droplets to be tailored to match the resolution requirements of the image. Measurements given in picolitres (pl) show the relative sizes of droplets for different resolution settings. (One picolitre is one trillionth of a litre.)
The ink sets used in low-cost printers are often supplied as one or two cartridges, containing between three and five coloured inks and a black ink. When one ink runs out, the entire cartridge must be replaced. This system is convenient for novice and low-volume users but not cost effective for photographers who wish to make lots of prints. Consequently, an increasing number of manufacturers now make individually replaceable cartridges for their photo printers.
The individually replaceable cartridges can be seen at each side of the front panel on this multi-function inkjet printer.
The most common photo ink set consists of yellow, magenta, cyan, light cyan, light magenta and black inks, although some manufacturers have added red, blue and green cartridges to increase the colour gamut and provide better colour and tonal accuracy. Others have increased the number of black cartridges, providing separate blacks for glossy and matte paper and/or a range of blacks covering light grey, mid grey and full black. Such ink sets significantly improve the quality of black and white prints by increasing the range of tones that can be reproduced and reducing the chance of colour abnormalities (see Setting up a Colour Managed Workflow).
The improved reflectivity produced by the additional resin layer gives prints a brighter, glossier appearance and helps them to resist surface abrasions.
Epson has added a ‘Gloss Optimiser’ cartridge to the ink set for its R800 and R1800 printers, which use resin coated pigment-based inks. This applies a layer of resin where there are no resin coated pigment particles on the print, providing a consistent reflectivity that makes glossy prints look even better.
Dye-based printers are usually faster than printers that use pigment inks. In the past, prints made with dye inks had a wider colour range and greater vibrancy than prints made with pigment inks. However, the latest pigment printers use inks that can match (or better) the best dye inks in colour gamut and saturation.
Prints made with pigment inks were formerly more stable than those made with dyes – but dye prints from some recently-released printers are now as lightfast as some pigment prints (although not as resistant to humidity and atmospheric gases). Both these factors make it important to read manufacturers’ claims carefully and look at actual prints before purchasing a photo printer.
The market for inkjet consumables (inks and papers) is wide and varied and cash-strapped photographers may be tempted to substitute alternative inks for the inks produced by the manufacturer of their printer. Some may even refill depleted ink cartridges to save money! However, there are some persuasive reasons to avoid third-party inks and stick with the inks developed by the manufacturer of your printer.
Very few third-party ink manufacturers have their inks independently tested on a range of popular papers and few can supply ICC profiles (see Setting up a Colour Managed Workflow) for their inks. Be very wary of companies that make extravagant claims for inks or papers – and those making claims that products are “the same as” or “equivalent to” printer manufacturers’ products. Check for genuine lightfastness testing (see below) before you purchase such products.
Three main paper types are used for inkjet printing: swellable, porous (or microporous) and cotton rag. Swellable paper has a coating that expands when it comes in contact with ink, allowing the inks to penetrate the top layers. Most consist of three layers: a protective top layer that prevents the dyes from spreading and excludes atmospheric pollutants; a layer that fixes the ink droplets in place; and below that, a layer that absorbs additional ink components. The paper base is sandwiched between two polyethylene layers (like traditional photographic papers) and backed by an anti-curl coating and an anti-static layer. Swellable papers should only be used with dye-based inks.
Porous papers are coated with microscopic inert particles that create cavities in the surface in which ink is deposited. These cavities prevent the ink from spreading. Porous paper has a higher resistance to moisture and humidity and is often referred to as ‘instant dry paper’. Because prints on porous paper have no protective polymer layer, the colourants are susceptible to attack by atmospheric pollutants. Porous paper is the preferred paper to use with pigment-based inks, which are less affected by atmospheric contaminants than dye-based inks. Pigment-based inks also have much better lightfastness characteristics and ozone resistance on porous papers than dye-based inks.
Cotton rag papers are generally used for ‘fine art’ printing because they provide excellent image quality and the longest overall print life on the market when used with pigment-based inks. Cotton papers are generally acid free and lignin free. Some manufactures add alkaline buffers for increased protection from atmospheric contaminants.
Although most printer manufacturers can provide a choice of glossy, semi-gloss and matte papers to suit their printers, photographers also have a huge range of third-party papers to choose from. It can be difficult to select high-performing papers that produce long-lasting prints from the multitude of papers on sale. However, because inkjet papers often perform differently with different inks and printer types, it is best – at least initially – to use the papers and inks recommended by the printer manufacturer.
Another reason to favour manufacturers’ papers is that they make it easier to select the correct settings for printing. As explained in the previous chapter, all printer drivers contain profile settings for the papers recommended by the manufacturer for use with that printer. These profiles usually cover a wide range of paper types, from plain office paper to top-quality paper for printing long-lasting photos. Matching the driver setting to the paper gives you the best chance of producing the highest quality, most colour-accurate and longest-lasting prints.
It is easier to be sure your prints will be long-lasting when you select papers from the printer manufacturer’s range.
Fine art photographers and those who want particular paper surfaces not supplied by their printer manufacturer may find it worth experimenting with some of the high-quality specialist papers. However, with so many different papers available for inkjet printing – and a wide range of printers to choose from – most photographers are likely to encounter problems with colour accuracy in prints on third-party papers, at least initially.
It’s tempting to try manually ‘tweaking’ driver settings to get better colour by process of elimination but, although this may improve colour reproduction, it can’t guarantee colour consistency from print to print or accuracy across a wide range of colours. Use of ICC profiles (see Setting up a Colour Managed Workflow) is the only way to ensure accurate printed colour for all colours a printer can reproduce so we advise photographers to choose only papers from manufacturers that make these profiles freely available. In most cases, they can be downloaded from the paper manufacturer’s website.
You need profiles for each step in the colour workflow to achieve consistent colour management. More information on this topic can be found in Setting up a Colour Managed Workflow. Achieving accurate colour via manual tweaking is nearly impossible due to the complex nature of printer colour response.
The Issue of Cost
It is common for photographers to compare the cost of inkjet media with that of older-style photo prints. In the past, the high cost of inkjet media put inkjet prints at a disadvantage. However recent developments have changed that situation and prints from some inkjet printers – on some papers – can be both cheaper and longer-lasting than equivalent photo prints. They may look better as well.
The resolution setting you use for printing can significantly affect printing costs. When resolution settings are excessively high, the output quality looks no better but over-inking increases the overall cost per print.
One factor that has made it easy for printer buyers to calculate per-print costs has been the trend for manufacturers to bundle papers and inks together and sell a complete consumables package. This is common for snapshot printers but is also beginning to be adopted for A4 models.
Tests by Photo Review over the past three years have shown a typical A4 inkjet print will cost between about $3 and $5.50. Most printers yield between 35 and 50 A4 prints before the first ink reservoirs are depleted so you can calculate an equivalent cost range for other paper sizes (you can produce roughly four times the number of 15 x 10 cm prints or one quarter the number of A3 prints with the same amount of ink).
When calculating printing costs, allow for at least 10% wastage to cover prints that are unusable through one or more of the following faults:
Print Lightfastness Testing
The durability of digital prints is now an important issue, with many paper manufacturers making claims about the longevity of prints on their media. This issue is vital for anyone who wants prints for display and everyone wanting prints to hand on to future generations because some ink/paper combinations are even more prone to discolouration than traditional photo prints. Colour changes can become apparent within weeks when some media are used and in months with others.
The good news is that some inkjet prints are much more durable than colour photo prints. When certain combinations of inks and papers are used, print lifetimes can exceed 100 years.
The most objective and reliable information on ink/paper stability can be found at the website of the independent testing institute, Wilhelm Imaging Research (www.wilhelm-research.com), where you can find details of procedures used to test and report on a wide range of traditional and digital media, along with information on specific printer/paper combinations. WIR has recently embarked on a certification program that allows manufacturers whose printers, inks and papers have been evaluated to label their products with lightfastness ratings.
Some manufacturers also conduct their own lightfastness tests. However, care must be exercised when looking at their results as these tests often differ substantially from Wilhelm’s standard procedures. It is difficult to compare these claims with Wilhelm’s published results for particular products and some of the ‘lightfastness’ claims equate to much shorter lifetimes in the WIR’s tests.
Lightfastness figures vary with different paper types and different ink sets so make sure you match the paper type to the printer you use.
The main factors that affect the stability of inkjet prints are the ink/paper combination and handling and storage conditions after the print has been made. 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 and both claim high longevity.
High quality, acid-free papers are more stable than standard papers, which is why they are used for all archiving and fine-art applications and most traditional photography. Pigment inks are also more stable than most dye-based inks.
The most common cause of colour changes in inkjet prints is a change in the dye chemistry due to oxidation. Certain paper/ink combinations are highly sensitive to ozone, which is common at low-levels in urban environments and reaches high concentrations around devices like refrigerators and air conditioners. This is why you should never display unprotected inkjet prints on the fridge door.
Light can cause differential fading, particularly with magenta dyes. Cyan dyes, on the other hand, are most susceptible to chemical contaminants and, as they fade, prints turn orange. To complicate matters, prints made on some papers can take several days to finally stabilise. This can lead to uncertainty about what the final print colour balance will be.
To obtain the maximum stability from your inkjet prints, give each print a minute or two to dry then cover it with a sheet of plain paper. Leave the covered print for at least 24 hours before framing it or storing it in an album. Inkjet prints last longest when framed behind glass or encapsulated in plastic (‘laminated’) to protect them against airborne pollutants. This is also a good way to protect traditional photos against light, dust and moisture – as well as airborne fungal spores.
Readers can download a guide to the preservation and care of colour photographs free of charge from www.wilhelm-research.com/book.html. Written by preservation specialist, Henry Wilhelm, the book covers both traditional and digital prints, colour negatives, slides and movie film. It is fully illustrated and provided in PDF format.
The illustrations show how a print on a less durable photo paper can change after six monthson display on a fridge door. Note the loss of the blues and greens in the faded image.