The Permanence of Paper
Top quality photo paper is often described as archival paper which relates to the estimated longevity of the photographs printed on that paper. However, the permanence of the final photograph will depend not only the the photo paper but also on the ink used to print the photograph as well as the environmental factors such as light, temperature and humidity to which the picture will be exposed.
Paper manufacturers do not guarantee the longevity of prints made using their photographic papers but they do provide estimates of longevity based upon the tests carried out by independent research laboratories using internationally agreed controlled conditions. For example, Epson estimates that its high quality Traditional Photo Paper used with Epson Ultrachrome K3 inks will last for 90 years with colour prints.
The Colour of White
Over time ordinary white paper becomes yellowish in colour and deteriorates. This is caused by lignin which is a structural component in the cell walls of the wood used to make paper pulp. Lignin is removed during the manufacturing process of archival fine art papers so that over the archival period the paper will not change colour or become yellow. Chlorine and acids are also removed from the pulp so that the structure and integrity of the fine art papers remains robust and does not deteriorate over the specified archival time.
Bright, white photo paper is required in order to obtain high contrast photographs with a wide range of colours. In addition, the brightness of the paper has a significant impact on the way in which the highlights in the image will be expressed. For example, the highlights will look different on very white paper compared to paper which is creamy in colour. In order to a obtain a bright white product the paper is usually bleached during the manufacturing process and optical brightening agents (OBAs) are added to ensure that the whitest whites in the image may be produced in the print. OBAs interact with UV light and fluoresce to emit visible light with a slight bluish tinge. This gives the paper a very bright white appearance. However, excessive use of OBAs may compromise the permanence of the paper and if the subject of the image does not require the brightest whites OBAs may not be necessary.
Photo papers have a coating on the surface placed above the base layer. During the printing process this coating rapidly absorbs the inks which then dry quickly. This prevents the inks from bleeding excessively such that the original sharpness of the image is sustained in the photograph. Some fine art papers have a baryta layer applied to the surface. This is a barium sulphate coating (from barite which is a natural substance like clay). Baryta papers are fibre based and made from materials such as cotton or linen rag (as against cellulose from wood) and rag papers are expensive. The baryta layer supports a very high definition and tonal range in the print and also makes the paper bright and smooth. Usually the baryta layer is used to add OBAs to enhance whiteness. A baryta layer provides the basis for very deep blacks and against the whiteness of the paper this ensures great contrast. They are particular popular for black & white photographs.
It is worth noting that glass interferes with the transmission of UV light and therefore when the fine art print is mounted and framed behind glass the effect of OBAs will be nullified.
The Colour of Black
The colour of black is critical to an image. If the deepest blacks in the image are insufficiently dark then the photograph will look weak and washed out. Consequently the depth of the black that can be printed on the photo paper is an important parameter. It is measured by Dmax which is a measure (negative log to the base 10) of light reflection by the deepest black that the printer can produce using specified inks on the photo paper in question. Gloss papers usually have a high Dmax with a value up to about 2.5 whereas matte papers have a Dmax of about 1.7.
The Weight of Paper
The weight of the paper is also of importance in that weight provides rigidity to the photograph and enhances its feel. It is measured in grammes per square metre (gsm). Ordinary paper is usually about 100gsm and fine art papers range from about 230gsm to over 350gsm. Heavy paper is usually thick paper and, whereas ordinary paper is about 0.2mm thick, fine art photo paper may be 0.5mm or more. However, not all printers are capable of accommodating such thick papers and printers for fine art paper usually have an additional paper feed mechanism to load paper at the front or the back so that the paper can pass the through the machine without being bent: these papers are often available only in sheets as against large rolls
The Surface of Paper
The choice of paper for your fine art print depends on a number of factors. Gloss paper has a very smooth surface whereas matte paper may either be smooth or have a structured surface which can add a small three dimensional perspective element to the picture surface. Sometimes the paper is neither gloss or matte, but rather in between the two and called lustre, satin or semi-gloss.
If the photograph contains numerous sharp edges with fine detail, their sharpness in the print will be best resolved by gloss paper whereas less focussed structures, as in landscapes for example, may be better represented on matte papers. Also gloss paper will have a greater tonal range than matte paper such that blacks will be deeper on gloss than on matte.
In photographs where the contrast and tonal range are of prime importance then perhaps gloss would be the paper of choice but if the image has a soft, ethereal perspective then on gloss paper it may appear too contrasty and matte paper might be more appropriate. However, the majority of images will look great on either gloss or matte fine art paper and paper selection is a matter of personal choice.
Having purchased a fine art photograph it is advisable to preserve your investment by mounting it in an appropriate picture frame which suits the style of the location in which the print will hang. This will protect the photograph from dust and scratches as well as from UV light which is particular damaging to print permanence. Normal glass used in picture frames will block over seventy five per cent of UV light and a specialist picture framer will be able to provide you a museum-type glass which contains enhanced anti-reflection properties as well as blocking over ninety nine per cent of UV light. This will ensure your fine art print will be enjoyed for many years not only by you but also by future generations.
Of course there are many archival fine art papers to choose from but it is worth noting that the Epson range of Signature Worthy Papers, (hot press bright, hot press natural, cold press bright, cold press natural, velvet fine art paper and traditional photo paper - called exhibition paper in America), although expensive, are especially impressive in sustaining brightness, colour and contrast in fine art prints. The results are superb.