by Daniel Rollins
Today we are surrounded by photographs, in magazines, on hoardings and through social media we are surrounded by captured light. In the age of the camera phone we are taking more and more pictures to share with friends and family, to record significant events or as a form of artistic expression. Many of these photos are shared on social media for the immediate pleasure of friends, family or acquaintances and are quickly (and in the case of some images gratefully) forgotten. Others however are used to archive scenes, people and events yet despite photograph's apparent stability, like any medium, photography is not permanent. Files corrupt, hard drives fail, social media sites shut down and the delete button is sometimes accidentally pressed. Older physical medium are equally at risk of damage or destruction, old prints fade or tear and negatives decay and degrade. The final scenario was the subject of my PGS Extend research project.
|Damaged negative affected by vinegar syndrome.|
Photographic film is made up of two main layers, the emulsion, which contains the photosensitive chemicals and holds the image, and the base which supports the thin layer of emulsion. Since the late 1940’s most photographic film has used a plastic called cellulose acetate, a safe, flexible transparent plastic, as a base. However after several decades of storage cellulose acetate breaks down, releasing ethanoic acid (the chemical that gives vinegar its taste and smell) and causes the film to become brittle and shrink, damaging or destroying the image. This degradation is called “vinegar syndrome” and is what Dr Rob Symmons, curator at Fishbourne Roman Place faced with his large collection of photographic negatives containing images fromthe excavations at the place during the 1960’s and ‘70’s when he began smelt vinegar in the boxes they were stored in. The most severely affected images were already destroyed when Guy Cripps and I visited him to see how we could help. As there is no way of reversing or stopping vinegar syndrome our task was to develop a way of detecting it before it reaches a critical level, giving him time to copy or digitalise the images.
The most obvious symptom of vinegar syndrome is the distinctive smell of vinegar given off by the ethanoic acid however at low levels this is undetectable to the human nose. Therefore we looked to find a simple chemical method of detecting the acid before you could smell it. To do this we used a solution of the acid-base indicator bromothymol blue and sodium hydroxide which is usually blue but turns yellow when acid is added. To make this indicator more practical we soaked strips of filter paper in the solution and left them to dry producing strips of blue paper which when we tested them in the box already smelling of vinegar turned quickly yellow. We then left some of our indicator strips with Dr Symmons and were emailed a few days later with the news that they had detected acid in another box not yet smelling of vinegar; thankfully that box has already been digitalised.
Vinegar syndrome is a problem in museums and film archives around the world yet many archivists and curators are unable to detect it before it is too late due to the sheer size of collections or the insensitivity of their noses. Yet simple chemistry can provide a simple and easy to use way to detect the breakdown of cellulose acetate and even provide an early warning to prevent damage to valuable or significant collections.
|An original negative|
|and its digital scan.|
Photos by Daniel Rollins