Park Photo Services - Fine Art Photography - Technical Notes for Collectors

Technical Notes

Park Photographic Services - Fine Art Photographs

Park Photographic Services

Technical Notes:

Image Permanence and Photographic Conservation

Introduction

Throughout this site you will find references to 'archival processing' and 'archival permanence'. This page explains the significance of these terms, and why they are important to anyone buying photographs. You may find it helpful to print the page for easy reference, or simply save it to your hard disk.

The information provided here has been gathered together from many different sources, and is given in good faith. To the best of our belief it is accurate and reliable but we accept no responsibility for errors, omissions or the general reliability of the technical information given here or elsewhere in this site.

Before important decisions are made about conservation matters, the information given in these pages should be verified by reference to specialist sources. (See our Bibliography section.) In the case of valuable photographs or collections, professional advice should be sought on storage, display conditions, and other matters affecting image permanence. Sources of such advice might include those museums that house substantial photographic collections, and the technical departments of major manufacturers of photographic materials.

The Problem

The question of archival permanence arises mainly because traditional photographic processes rely almost entirely on the sensitivity of certain silver compounds to light, which causes their chemical structure to change. Without this special chemical property, photography as we know it would not exist. But sensitivity to light is a two-edged sword.

If you look at almost any old photograph - especially one that has been kept on display - you will probably see evidence of fading or other deterioration. This is partly because of the general bleaching effect of ultra violet light but damage also arises because of residual light-sensitivity in the silver compounds which make up the image. Image deterioration may not be apparent for many years but prolonged exposure to light, especially where combined with flaws in the original processing technique, will inevitably lead to deterioration.

Thorough chemical fixing (using sodium thiosulphate or similar fixing agents) is important, but provides only part of the answer because, without the most thorough washing, residual traces of fixer can also lead to fading of the image, and can also cause chemical staining.

Other sources of damage or deterioration include the effects of acids in the photographic paper or mount-board, chemical breakdown of adhesives, fungal growth in the gelatine of the emulsion, or the effects on the print of sulphur compounds or other chemical pollutants in the atmosphere.

Possible Solutions

If all this seems sad and depressing, do not despair. Photography is now over 150 years old, and the fact that significant numbers of early photographs are still around for us to enjoy shows that long term preservation is perfectly possible, provided we start with the right materials and processes and take a little care to avoid chemical contamination at the processing stage - or any other stage, for that matter - or storage in unsuitable conditions. Museums and art galleries have lived with this problem for many years and a body of expert technical knowledge has gradually emerged.

Fibre-based Printing Paper

If a photograph is to last a lifetime (and if you are an investor in photographic art, you will want it to last at least a lifetime) the first requirement is that it should be printed on good quality photographic paper - preferably on a make or type of paper that has a proven track record.

Modern resin-coated papers are excellent. They are a pleasure to use and can produce beautiful prints but, despite assurances from the manufacturers, there is still a question mark over their long-term survival. This is not a criticism of the manufacturers. It is simply that these papers have only been around for 20 years or so, and in that time specifications have been changed several times. There is, as yet, insufficient evidence to demonstrate that this type of material will survive for 50 or 100 years, and yet many of today's photographs may be of greatly increased value in 100 years time - provided they survive.

While manufacturers claim, on the basis of 'artificial ageing' tests, that resin coated papers now have a very high level of permanence and stability, it is far safer to rely on materials that have been used successfully over a long period of years. Scientific testing is important, but the test that really counts is the test of time.

Archival Processing

The second requirement for archival permanence is that the photograph is properly processed, fixed, washed, and dried. Adequate chemical fixing is clearly important because without it the silver compounds in the image will be unstable, and will remain sensitive to light. Washing must not be skimped because fibre-based paper absorbs large amounts of fixer, and all traces of this this must be removed if the image is to remain stable over a period of many years. Surprisingly, drying methods are also important because excessive heat may cause microscopic cracking of the paper's emulsion or supercoat. Air-drying at normal ambient temperatures - preferably on screens of fibreglass mesh - is now the recommended procedure for archival results.

Chemical Toning

To give an even greater assurance of permanence, the image should also be toned. The purpose of toning is sometimes to alter the aesthetic appearance of the image but, even when no change in tone or colour is required, toning is still an important stage in the production of a Fine Print. This is because, for a high level of permanence, silver salts in the image should be converted into other compounds, with chemical structures that are not unduly sensitive to light.

Archival Mounting

Most types of mount-board, including the majority of boards available from Art Supply shops, are made from mechanically ground wood-pulp and are not of genuine archival quality. That is to say that, while their appearance may not change for a number of years, the long-term prognosis is that they they will tend to become yellow and brittle. Even worse, unless the board is guaranteed to be acid-free (the most basic of archival requirements) the acid content of the fibre may well contaminate the photographic print.

The most satisfactory mount-board material for photographic use is known as 'museum' board. This is made entirely from cotton rag fibre rather than wood pulp and is available in 'buffered' form (i.e. with a pH value slightly on the alkaline side of neutral) or 'unbuffered' (i.e. with a neutral pH value). The buffered version is preferable for most photographic purposes but the 'unbuffered' version is required for certain types of print - including albumen and dye-transfer prints - which require a neutral pH environment.

Photographs should ideally be mounted onto a substantial sheet of museum board - say 1500 microns ( 1000 microns = 1 millimetre) or more - and protected by an overmat of traditional 'window' design cut from the same material. This allows an air-space between the print and the glass, thereby preventing 'ferrotyping' of the image or the harmful trapping of moisture between the surface of the print and the glazing material of the frame. Mounting the print may consist simply of 'sandwiching' it between mount and overmat, using paper hinges to hold it in place. More controversially, it may involve the use of an adhesive to fix the print to the mount (see below).

Mounting Adhesives

The choice of adhesive for photographic mounting is particularly controversial area, and a subject that has caused many photographers to search their souls. The main issues are dealt with in this note.

The ideal mounting adhesive for photographic use has the following properties. It is easy to use, provides a strong bond between print and mount, does not deteriorate with age, contains no chemical compounds which might react with the photograph or mount, and does not support bacterial or fungal growth. Also, in case the worst should come to the worst, the adhesive should be 'reversible' - in the sense that it should be possible for the print to be removed, without damage, from a soiled or damaged mount.

Based on these criteria, most popular adhesives are quite clearly 'out' as far as archival permanence is required. These include virtually all adhesive tapes, aerosol sprays, traditional (bone-based) glues, rubber cement and all proprietary versions of these materials. However, if a firm decision has been taken to mount the print, there are other adhesives which may be regarded as acceptable. This group includes wheat starch, rice starch and possibly one or two other 'natural' adhesives, all soluble in water. Neutral pH PVA adhesive is a more modern alternative, also widely accepted and also soluble in water.

A particular difficulty arises when it comes to the popular photographic 'dry-mounting' process. For many people this is the most aesthetically pleasing mounting technique of all - involving the use of dry-mounting tissue in a heated press. The process is very clean and simple, producing a very flat surfaced print - free of the distracting surface 'undulations' sometimes seen in prints which are simply 'hinged' onto the mount. Dry mounting does, however, bring with it its own problems.

While most leading brands of dry-mounting tissue are unlikely to cause serious archival problems, and some have been used by very eminent producers of photographic art - including famous American landscape photographer Ansel Adams, the problem is that they cannot genuinely be described as 'reversible'. Although it is true that for a short time many types of tissue can be released by re-heating in a press, eventually - after a period of months or years - the adhesive bond 'cures' and is then almost impossible to release without causing damage to the print. A valuable print attached to a damaged mount then becomes an aesthetic disaster for which there is very little remedy.

At Park Photo Services, we have settled on a compromise. If we use an adhesive at all, we use unsupported Archibond. Unlike normal dry-mounting tissue which consists of a paper tissue base coated on both sides with heat sensitive adhesive, this material is simply a very thin sheet of pure unsupported adhesive which melts in a dry-mounting press but, most importantly, can be dissolved by immersion in spirit, should the need arise.

Unsupported Archibond is not particularly easy to work with as it cannot be 'tacked' to both the print and mount in the normal way, but it does produce a strong, clean bond and possesses most of the advantages of dry-mounting tissue with the added bonus of being reversible. Until something better comes along, we propose to stick firmly with this particular type of adhesive - if you'll pardon the pun.

Framing

Unfortunately, in terms of archival permanence, frames can also present hazards. Ideally, frames for photographic use should be made from materials which do not contain acid compounds, paints, varnishes, resins or other elements which might cause chemical 'migration' and reaction with the mount or even the print itself. Wooden frames made from cedar or pine are to be avoided because of their high resin content. Anodised or lacquered metal frames are probably the best.

Frames should be glazed with suitable - say 2 to 3 mm - glass or acrylic sheet ('Perspex' or 'Plexiglas'). Glass is the traditional glazing material for frames. It is cheap and scratch-resistant but presents a risk of damage to the print if it become cracked or broken or, particularly if it is shattered as a result of being dropped. Acrylic sheet is much more forgiving, being lighter and much less likely to shatter. It is however more prone to scratching if not carefully handled, and may also need an occasional wipe over with anti-static fluid to help prevent the attraction of dust. Some grades of acrylic sheet also have built-in u.v. screening to reduce the effects of ultra-violet light. This does not however mean that liberties can be taken with the normal guidelines about displaying photographs away from sources of bright light.

Whatever glazing material is used it should of course be clean - chemically as well as visually. It should preferably be cleaned with a 50:50 mixture of IMS (wood alcohol) and water and carefully dried with a paper towel. Alternatively it can be washed in warm soapy water, then thoroughly rinsed and dried with a clean cloth or paper towel before the frame is finally assembled.

Frame backs are usually made from hardboard (US 'Masonite' ) - generally of a special type which is thinner than normal 'DIY' (US 'Home Depot') grade and is smooth on both sides. Hardboard is a relatively harmless material but, to ensure that the back of the mount remains free from any possibility of contamination, it is probably best to place an additional sheet of archival material such as polyester (e.g. 'Melinex' or 'Mylar'), thin mount-board or strong cartridge paper - between the mount and the frame back. (Paper-based materials used for this purpose must of course be acid-free.)

If all of this seems excessively fussy, try taking a careful look at some old photographs, posters or prints which have not been preserved in this way. Signs of damage will have begun to emerge after a relatively short period of years.

Storage and Display

In a museum or gallery environment, photographs (like paintings) are normally displayed and stored in conditions of controlled temperature and humidity. They are also carefully shielded from exposure to daylight or bright artificial light. Around the home, a less stringent approach must be adopted, but the same broad principles apply. Pictures should not be exposed to extremes of temperature, humidity or air pollution. Prolonged exposure to bright light should also be avoided.

Colour Prints

Most of the information set out in these notes is aimed at collectors of monochrome rather than colour photography. This is because monochrome work still makes up the great bulk of collectable (actual or potential) photography, and also because very much the same principles apply to the conservation of colour photography as apply to black and white.

The dyes used in many colour printing processes do, however, introduce additional problems. These dyes fade noticeably with prolonged exposure to light, and the most common type of colour print - the 'C print' - is probably the most unstable. Most of us have a drawer full of 'C print' family photographs which have survived over the years because they have been kept in what is termed 'dark storage'. Where they have been left on open display the story is probably rather different. Recent developments in colour-paper technology have, according to the manufacturers, greatly improved the stability of 'C prints' but most collectors would still be wary of spending large amounts of money on a 'C print' image which might prove to be unstable.

Traditionally, the 'Rolls Royce' of colour printing technologies was Dye-Transfer Printing (not to be confused with the 'thermal dye-transfer' or 'dye sublimation' process now used by some digital colour printers.) Because this manual process gave the printer a great deal of control over the subtleties of the print, it could produce results of outstanding visual appeal as well as outstanding permanence. Dye transfer printing is however a fairly complicated hand craft, and many times more expensive than most other processes. As a result, the demand for specialist dye-transfer printing materials fell off over the years and the main producer of these materials, Kodak, recently ceased production. Now, alas, the process is largely of historical interest.

Digital colour printing - using ink-jet, colour-laser, or other computer-controlled colour processes - has come into prominence in the last few years and would appear to be the natural successor to dye-transfer printing. This technology is developing rapidly and suitable colour printers are beginning to emerge at affordable prices (rather than the heart-stopping prices seen at the top end of this particular market). Despite the beautiful results which can be produced by digital methods, we have not yet reached the stage where digital prints can be recommended with confidence to collectors who wish to avoid unnecessary risk of image deterioration.

One of the most appropriate colour technologies from the collector's point of view is that of Ilfochrome (formerly called Cibachrome, and re-named for corporate reasons). This is a reversal rather than a negative/positive colour process, directly producing a positive print from a transparency. Through the use of an inter-negative it can also be used to produce a positive print from a negative original. The attraction of Ilfochrome (or Cibachrome, as many people still prefer to call it) is that it produces prints of excellent colour saturation and contrast, and truly outstanding permanence.

Because it is not an overly complex process from the printer's viewpoint, Ilfochrome is also reasonably affordable and is the process chosen by Park Photo Services for reproduction of our standard colour images.

Although it will be seen from the above that, in terms of archival permanence, some colour processes are greatly preferable to others, all colour prints should be treated with care and not unduly exposed to bright sunlight, or even long periods of bright artificial light. Truly valuable items are probably best kept in cool dark-storage and brought out for display only from time to time.

Our Policy on Permanence

It is not always easy to know what images will acquire long-term value in the marketplace. Occasionally an image from a 'name' photographer may be bought at considerable expense and, in investment terms, may turn out to be a total 'turkey'. On the other hand, an image from a relatively unknown photographer, acquired simply as home decor rather than as a financial investment, may with luck appreciate significantly in value over a period of years.

While there is always an element of risk in buying pictures, it seems to us is that there is little point in buying photographs which are badly produced and potentially unstable. These pictures, however appealing, will rarely appreciate in value because their permanence will always be in question.

Our Fine Art Photographs are therefore produced to the highest possible archival standards - having regard to all of the issues discussed in these notes - and carry, on the reverse of the mount, full details of the materials actually used. Where these are not identical to materials specified in advance (e.g. in our Picture Gallery specifications), we guarantee that they will be of a quality at least equal to that originally specified.