There is a world of difference between pigment inks and soluble dyes. The inks used in the posters we sell are pigment inks. And that is how we are able to offer posters that have archival quality. That means they will remain bright and vivid for many years. That is provided they are kept away from direct sunlight and cigarette smoke, advice that applies to all printed material. Before we get to that though, lets take a step back in time to early black and white photographs.
By the way, if this poster takes your fancy you will find it and other wildlife posters in this section of Flying Twigs.
Black and White Photographs
Black and white photographs might be stored in a shoebox for seventy years. Yet they will probably look as good today as they were when they were printed.
The reason old black and white photographs don’t fade is that the image is made of silver compounds. We all know that precious metals such as platinum, gold, and silver, don’t react with the atmosphere very much. Compare that with, say, iron that rusts if left in the open air.
Of the three precious metals I mentioned, silver is the most reactive, and will turn a dark grey eventually if left exposed to the atmosphere. That is why the silver in black and white photographs are protected by a gelatin layer. And the paper in traditional black and white photographs is fibre-based paper, which is very stable..
Of course, the photos in that drawer or shoebox may be creased or rubbed. But if they were put away carefully that may be all the protection they ever needed.
The process used with film in the ‘wet’ darkroom is that light is shone through a negative onto the paper. The negative is of course the film that was in the camera that took the photograph. shining light through the negative produces a latent image on the paper. It is called ‘latent’ because it is invisible to the eye and must be developed, as it is called.
That latent image is put in a bath of liquid developer until the image appears. Once that happens the paper is transferred to a bath of liquid ‘stop’ that stops the reaction. If the paper is not placed in a bath of liquid ‘stop’ then the reaction will keep on going when the paper is exposed to light, until eventually the paper is entirely black.
Stopping the reaction is the first stage, but it then needs to be ‘fixed’ by placing the paper in a bath of a third chemical – and that’s it. And the whole process takes just a few minutes.
The thin layer of silver compound protected by a gelatin layer will remain stable for a hundred years or more.
If black and white photographs fade, it is probably because they were not processed properly.
For example, the chemical that stops the reaction may have become weak or exhausted. That means that the development carries on slowly over the years and darkens the photograph.
Resin Coated Papers
In the 1960s, plastic resin-coated papers for the amateur market were invented. Fibre-based papers use barium sulphate as the white base. Resin coated papers used titanium dioxide, a cheaper material, for the base.
The problem was that the titanium dioxide in the paper reacted with even very low levels of light. And that reaction produced peroxides. They oxidized the silver and darkened the photo over time.
A black and white photograph printed on a fibre-based paper in the 1920s may look new even today, while a resin-coated print made in the 1970s may look dark, lacking whites and high-key tones.
Colour Photographs from the 1970s
Colour photographs are made from silver compounds and clouds of dye set into an emulsion. The dyes are activated by light, and when the process is finished the silver is removed leaving just the dyes.
Early colour photographs were unstable, and after development the chemicals continued to react with each other. They also reacted and with the paper itself. And if that wasn’t enough, they also reacted with sunlight and the pages of the albums. You may well have seen colour photographs from the 1970s with the colour washed out.
Environmental Risks to 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. Therefore it pays to know what the biggest risks to the stability and vibrancy of colour photographs are. The two biggest risks 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 is to protect the photograph with a sheet of glass with a UV filter in 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.
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 made from materials that do not contain acids (such as paper made from cotton rag). Or they have buffer chemicals in them that counteract the lignin acids that are found in wood pulp.
Photographs Use Light To Activate Chemicals
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 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 develop the image and then to stop the development when the image is complete.
Prints and Posters
Prints and posters are different. The printer reads the information in the digital file and sends colour (pigment inks and soluble dyes) to the paper. So it is not light that acts on the paper and so the finished print is not a true photograph.
Inkjets and giclee prints are made by print heads that are controlled by computers that squirt colour onto the paper. And that colour may be a dye or a pigment.
Pigment Inks and Soluble Dyes
Dyes are solutions of dye materials 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 materials suspended in water. That is, pigments do not dissolve in water, they are suspended in it. 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 vaporize coloured dyes into the paper.
The distinction between dyes and pigments is important because it affects longevity.
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. They are now so stable that they rival true photographs for archival stability.
And why not, because pigments are what artists have used for centuries, bound up in oil to create oil paintings.
As we said at the outset, there is all the difference in the world between pigment inks and soluble dyes. The inks used in the posters we sell are pigment inks. And that is how we are able to offer posters that have archival quality and will last many years.