My name is Alice Jones and I am studying for an MA in Preventative Conservation at Northumbria University.  As part of my student placement I volunteered in Leeds University Library’s Special Collections.

Under the direction of the Conservation and Collections Care Team I have undertaken a project to conduct materials research on First and Second World War hats in the Liddle Collection. One of the project’s aims was to analyse and identify degrading hat linings in order to help us draw conclusions about why they have degraded.  Another aim was to produce a bespoke storage solution to minimise the chemical decay.

We first surveyed the hats in order to make a visual assessment of the condition of the lining materials and to discover more about the structure of the objects. We observed that the lining was not degrading in all the hats, but that some seemed to have darkened, become sticky and even brittle.

LIDDLE/MUS/1939-45 BA/13a, Officer’s Service Dress cap, 1939-45 period, worn by Lt. Col. F. J. Hebbert RAMC. Image credit Leeds University Library.

We wanted to find out why these particular lining materials were put into the hats.  Our research has shown that the linings might be made from silk which is a protein fibre, or rayon, a cellulose fibre often called ‘artificial silk’. The fabric was possibly treated with oil, hence its name: ‘oil silk’ fabric.  This was sometimes whale oil or later petroleum-based oil.  Fabric may have been prepared this way to provide a sweat shield.

It is possible that additional factors have played a part in the degradation. For instance, the amount of use a hat had – somebody may have served all through the war wearing the same hat or only been called up in 1944.  Other relevant factors could be the location where the individual served – for example North Africa or the Far East, which would have caused increased sweating – or even hair products such as macassar oil, pomades, Brylcreem and so on.

Originally we thought the lining material could have been the early plastic, nitrocellulose, but initial analysis seemed to suggest otherwise.  We used A-D strips to test for this.  These paper indicators turn from blue to green or yellow in the presence of organic acid vapours.  Contact acidity was detected from the leather headband, probably from the tanning process, but the lining did not seem to be emitting nitric acid vapour.  This vapour is produced by degrading nitrocellulose, therefore we ruled this out as the lining material.

A-D strip inside one of the hats from the Liddle Collection. Image credit Leeds University Library.

We are also considering carrying out Fourier Transform Infrared Spectroscopy (FTIR) analysis to help identify the chemical make-up of the linings. The technique uses infrared radiation to produce spectra which represent the molecular absorption or transmission of the sample tested. This requires reference spectra to positively identify the materials used for the hats.

The team hopes to obtain a new sample from Herbert Johnson milliners, who still make hats for the military, to see what can be derived from this technique.  The analysis is destructive so the ethics of taking samples from the hats must be considered.  Fortunately, there are some detached pieces of lining material from one hat we can use to reveal more about this fascinating phenomenon.