Originally published March 11, 2009
Black and white photographs that have been stored in a shoebox for sixty or seventy years may be as clear and unfaded today as they were the day they were made.
The reason is that the image in black and white photographs is made of stable silver compounds protected by a gelatine layer on fibre-based paper.
As we know, precious metals like silver and gold do not react with other materials – hence gold and silver jewellery. Silver is more reactive than gold, so photographic prints are protected with a gelatine layer.
Of course, photographic prints may have been creased or rubbed. But if they were put away carefully that may be all the protection they needed.
These photographs are not digital prints but prints made with film and printed in a ‘wet’ darkroom. And for that, the process that is used today is more or less the same as that from seventy or eighty years ago.
In a darkroom, light is shone through a negative onto photographic paper to produce a latent image. The latent or hidden image is then developed in chemicals so it can be seen.
To develop and fix the print, the paper is placed in a bath of liquid developer until the image appears. Then the paper is transferred to a bath of liquid ‘stop’ that stops the reaction. The third stage is to fix the print by placing the paper in a bath of a third chemical.
The whole process takes just a few minutes.
And the resulting thin layer of silver compound that is the photograph, protected by a gelatine layer, will remain stable for upwards of one hundred years.
That is not to say that all black and white photographs will be in perfect condition – but if they are not it is probably because they were processed incorrectly in the first place.
For example, the chemical that stops the reaction may have become weak or exhausted so that the development carries on slowly over the years and darkens the photograph.
Sepia Toning
The process can be taken a stage further using chemicals that make the print even more stable. One method replaces the metallic silver in the print and leaves the print with a sepia tone and is therefore called sepia printing.
The first stage is to remove the metallic silver using a solution of potassium ferricyanide and potassium bromide. The remaining form of silver is then converted to silver sulphide by bathing the print in a solution of sodium sulfide or thiourea.
Gold Toning
Gold toning does not turn a print to a golden colour. Instead a gold toned print is a cool, slightly blue colour. Whether to sepia tone or gold tone is an artistic decision. Both improve the archival quality of the print.
The first stage in gold toning is to bathe the print in gold chloride that replaces the silver in the print with gold ions. Buffering solutions are then used to stabilised the print but bathing in gold chloride is basically the whole process.
Gelatin and Gelatine
Gelatin and gelatine are different spellings of the same material, which is a protein derived from collagen. Gelatine is the preferred American English spelling. Gelatine is the British English spelling.
Resin coated papers
There is a proviso to all this, and that is that with the introduction of plastic resin coated papers for the amateur market in the late twentieth century, new problems arose. Traditional fiber based papers used barium sulphate as the white base. Resin coated papers used titanium dioxide.
And the problem was that the titanium dioxide in the paper reacted with even very low levels of light to produce peroxides that oxidised the silver and make the photo darker than it was when it was first developed.
So resin coated prints from only a few years ago have problems to which traditional fibre based prints are immune.
What we know from all of this is that the stability of the image depends on the materials that the image is made from, and also from the paper on which the image is made.
Colour Photographs from the 1970s
Colour photographs involve clouds of dye that are set into the emulsion along with silver compounds and the dyes are activated by light. When the process is finished there is no silver left in the image – just the dyes.
Colour photographs were, of course, introduced to the consumer market much later than black and white photographs, and the early compounds were not stable. They reacted with sunlight, with chemicals in the paper of the pages of the albums in which they were put, with cigarette smoke, with the paper the emulsion was laid on, and not least of all with each other.
And colour photographs from those days will probably have faded very badly. Some are now no more than a pale smudge.
Modern Colour Photographs
Thankfully, there have been big advances in colour materials and modern photographs have archival stability to rival black and white photographs.
That is not to say that colour photographs are immune to deterioration, and it pays to know what the biggest risks to the stability and vibrancy of coloyr photographs are, which are sunlight and chemicals.
There are two ways of preventing sunlight damaging a photograph. The first is the obvious one, which is to hang the photograph out of direct sunlight. The second way is to protect the photograph with a sheet of glass that has a UV filter within it.
That is an expensive option and there are other downsides, because the colours of the print may look somewhat muted behind UV glass. And of course, many people don’t want to put glass over a photograph at all.
Chemical Attack
Cigarette smoke and cooking fumes pose perhaps an obvious risk. But there may also be corrosive chemicals in the materials with which the photograph is in direct contact. The wrong kind of mounting board can attack the print. The board may be made from wood pulp that contain acids that interact with the print. They can cause it to turn yellow and eventually destroy it.
A good framer will know this and will use an acid-free mounting board. These boards are either made from materials that do not contain acids (such as cotton rag) or they have buffer chemicals in them that counteract the lignin acids that are found in wood pulp.
Giclees, Inkjets, and Dye Sublimation
True photographs use light to activate chemicals in the paper. That light may be focused onto the paper in the traditional way with an enlarger. Or the light may be focused digitally with a laser that reads the negative (or even a digital file) and shoots light in a controlled pattern onto the paper.
Whichever method is used, the clouds of dye and silver compounds in the emulsion are activated by the light, and chemicals are used to develop the image and then to stop the development when the image is complete.
New Printing Methods
At the same time that the colour materials found in true photographs have been improving to the high quality we have today, there has been a movement in the home market and the professional fine art market with consumers and photographers printing their own photographs with new digital methods.
These new kinds of prints are not true photographs because they do not use light at all. Instead the printer reads the information in the digital file and uses that information to send colour to the paper.
Inkjets and giclee prints are made by print heads that are controlled by computers and which squirt materials onto the paper. The materials may be dyes or pigments.
Dyes are solutions of dye materials in water; which means that the dye is dissolved in water and the solution is squirted onto the paper and absorbed into it.
Pigments on the other hand are suspensions of very finely ground insoluble material such as stone that is suspended in water. The suspension is squirted onto the paper and the pigment lays on the surface of the paper rather than being absorbed into it.
Dye sublimation prints are a third option that use a heated head to vaporise coloured dyes into the paper, and these are generally not able to produce as detailed a print as other methods.
The distinction between dyes, which are absorbed into the paper, and pigments that do not dye the paper fibres is important.
Dyes are not colour-fast and can fade within a matter of months. Pigments on the other hand can remain light-fast for upwards of 100 years, and are now so stable that they are said to rival true photographs for archival stability. And why not, because pigments are precisely what artists have used for centuries, bound up in oil to create oil paintings.