Conserving a Second World War Bomb Map of Norwich by Yuki Russell

In 2007, a Second World War bomb map of Norwich was relocated from storage at the Norwich City Engineering Department to the Norfolk Record Office at the Archive Centre (Norwich, UK) for permanent archival storage. The item had been one of the most popular maps in the collection: any public exhibition of the item has typically been followed by increased requests for its use and repeated trips from storage.

At the end of 2012, the decision was taken to conserve a Second World War bomb map of Norwich (UK). The map was created by the Norwich Air Raid Precautions Department during the war, featuring 679 paper labels marking the bombs which fell on the city from 1940 -1944. The location of each label represents the site, date and size of each bomb.
Repetitive handling of the original was caused by the lack of a usable digital image. The condition of the map was such that, no adequate facsimile could be made despite several attempts at capturing a quality, detailed image. Hence, one of the main objectives in bringing the item to conservation was to produce a digital surrogate.
The strong demand for digitisation prioritised conservation of the map, though the very poor condition alone easily justified conservation treatment with some archival information being at serious risk of permanent loss.
At 188cm high, 182cm wide and 8cm deep, the map was comprised of three separate ordnance survey maps. The conjoint sheets were directly mounted onto two wooden fibreboards with a wooden strainer. Interestingly, the map contained 679 small paper labels attached with metal pins. Many being heavily distorted, the numerous labels were certainly a factor in obstructing previous endeavours to produce a clear digital image, with information written on them not easily captured by the camera. The metal pins held the labels were corroded to various degrees. Corrosion was believed to be the result of the various organic acids emitted from the poor quality fibreboard and inappropriate environmental conditions, especially those under which the map was previously stored.
The chief concern was discolouration, with the map appearing extremely darkened throughout. The entire verso of the map was in contact with the poor quality wooden backing board, suggesting the paper had been oxidised by volatile organic compounds (VOCs) and other types of organic acids generated in the board.
On the reverse of the backboard, the sharp ends of the pins were protruding through the board, which necessitated extreme care in handling especially during transportation from storage.
The main obstacle to viewing this vital archival information however, was the distortion of the labels and the method by which they had been mounted. Additionally, densely clustered labels in certain areas (representing severely bombed locations) further obscured the data.

ASSESSMENT AND TREATMENT PROPOSAL

The scale and complexity of the item required me to establish the best conservation approach, weighing the benefits of various degrees of intervention against time constrains. As part of this assessment, the individual labels were categorised by condition, allowing me to prioritise their treatment. The markers were therefore divided into the following groups:

• Approximately one quarter of the labels and their pins needed to be replaced urgently as they were at risk of becoming detached from the map.
• Approximately one quarter of them needed to be flattened, as they were distorted to various extents and were illegible.
• The remainder, though firmly attached and flat, were illegible and showed signs of deterioration such as corrosion spreading through the paper.

The other major concern regarding the stability of the item was the presence of the wooden fibreboard. Composed of poor quality materials, the structure adhered to the entire verso of the map leaving it exposed to potential further deterioration - leaving the backboard untreated was therefore considered seriously detrimental to long-term preservation. However, replacement of the board would necessitate removal of all labels and pins.
Taking these facts into account, two separate treatment options emerged:

• The first option was to minimise treatment with the focus being on digitising the map.
• The second option was a more comprehensive programme involving stabilising the paper labels and replacing the backboard to achieve a long-lasting improvement in the condition of the map.

Choosing the first option would imply that the fundamental causes of the gradual deterioration would remain. The benefit of the second option was the stabilisation of the item as a whole. Prioritising long-term preservation was clearly the route by which to proceed. However, the removal of the 679 labels would be a considerably more time-consuming treatment compared to the first option.
I had serious reservations regarding the first option: once superficial work had been carried out and the necessary digital images obtained, it was feared that genuine conservation work would no longer be a priority, with further work being postponed indefinitely. Once the demand for a usable digital image was met, was it possible that the condition of the item itself might be disregarded over time? It was infact the need for digitisation that led to the map to be earmarked for conservation in the first place. Mindful of these risks, it was therefore established that the more comprehensive programme of treatment was the most favourable approach to the item and the situation.

CONSERVATION TREATMENT

After establishing a means of safe handling of the labels throughout the project, all labels and pins were removed. This removal enabled access to the structure of the map.
Writing media permitting, washing the map was the preferred cleaning method. However, aware of the risk of causing dimensional change in the three individual sheets, this was eventually decided against. Therefore, surface cleaning was chosen along with tear repair and lining of the whole map.

Each label was washed individually in a small container in order to ensure identification at any stage during washing.
After washing, alkalisation with calcium hydroxide was undertaken. The labels were then flattened and lined with two layers of Japanese paper. In addition to discoloration, the original locations of pin-holes were a serious issue as these were located extremely close to the text (sometimes even obscuring it) or at the very edge of labels. In some cases, due to the miss-location of holes, pinheads and rust stains, information contained on the labels was rendered illegible. The lengths of the worse affected labels were extended in order to accommodate the new pin holes and to reattach them to the map. The extension was made with two layers of Japanese paper. The entire reverse of each label was then covered with a Japanese paper dyed with direct dye in order to blend the new extended segment with the original brown-coloured label.
In selecting a new backing board, a Tycore™ Support Board was employed. With its honeycomb cell structure, Tycore™ boards were chosen not only for quality and long-term stability but also assured low weight of the complete assembly without compromising rigidity.
After reattaching the wooden battens to the new backboard and despite the belief that the map would be used less once digitised, as the intention was to store the map vertically, it was critical to make sure that tension of the whole map was sufficiently maintained. Heavy weight Japanese paper hinges were therefore attached equidistantly along all edges in order to firmly tension the sheet in all directions. The outer strainer was then reassembled using new stainless steel screws.
Despite the complex and extensive procedures of preparation and treatment up to this point, the remaining tasks were relatively straightforward. By referring to a location map of labels made prior to treatment, the labels were returned to their original locations. New stainless steel pins, thinly coated with Paraloid B72, were used to replace the original corroded pins. One significant improvement was the visibility of written information with the replacement pins being relocated at the newly extended edges where the labels were previously severely damaged.
An additional backing of Plastazote® was added to the back of the new board; this was done so that the sharp ends of the pins which were previously protruding through the board were adequately supported and covered, both securing the labels in place and assuring safe handling.
On completing treatment, a bespoke packing was made for the map. An oversized four-flap enclosure was produced using Tyvek® sheet. In addition to the external cover, the recto was covered by two corrugated plastic panels. Previously, the item was simply wrapped in a single, large sheet of Tyvek®. Due to the size and nature of the map, the Tyvek® easily snagged on the distorted paper labels when uncovered and so the problem was resolved by the new protective panels.
Finally, digitisation was carried out with whole and detailed images being made available to the public. Conservation of the paper labels contributed significantly to the production of a clear image of each label. The original map is now stored in a controlled environment with handling kept to an absolute minimum.
All of the digital images are available in CD and can be purchased through the Norfolk Record Office website (http://www.archives.norfolk.gov.uk) or accessed using the computer terminals in the search room.

Yuki Russell
Since completing the second MA in Conservation of Works of Art on Paper at the University of Northumbria in Newcastle (UK), she has been working within the Conservation Section of the Norfolk Record Office at the Archive Centre.