Conservators are often likened to doctors: they examine their ‘patients’ (the ailing documents), recognize the symptoms, diagnose a disease and prescribe and administer a treatment which will restore them to health without altering their nature or disfiguring their appearance.
I was mindful of the comparison as I worked on the document above for the current winter exhibition, Plague! at the National Library of Scotland. It proclaims the government prohibition on trade with England in 1665, in order to prevent transmission of the disease across the border.
Over time, it had accumulated dirt and become discoloured. At some point it has been folded – the four folds can clearly be seen in the image, together with some tears and cockling. Lastly, the document bore little manuscript annotations in iron gall ink – a metallic composite of water, gum Arabic, and iron sulphate, combined with tannins from oak galls. This ink was extensively used from late antiquity until the early 20th century, and its ingredients cause deterioration of the material to which it is applied, sometimes called “ink burn”.
The document was removed from the volume into which it had been pasted, and gently cleaned with a brush and vulcanised smoke sponge.
The annotations tested positive for free iron II ions in the ink. Their presence is undesirable, because they catalyse cellulose oxidation and cause molecular chains to break, leading to perforation of the paper. In order to remove the discolouration and the harmful ions, the document was gently humidified and washed to dissolve water-soluble material; but first, a water-sensitive Library stamp on the reverse was treated with cyclododecane. This wax, when applied to an object, provides temporary consolidation and sealing of water sensitive media, protecting them while aqueous treatments are carried out, before subliming at room temperature, automatically removing itself from the object over a period of days after its application. This allowed the document to be washed without risk of the stamp bleeding. A micro-test made on the inks after the treatment showed that the free iron II ions had been removed (see the images of the test strips below). The paper was then humidified, relaxed, flattened and mounted on museum grade board, ready to be installed.
The document can now be seen its healthy state in the Government section of the Plague! Exhibition, which will be open at the National Library of Scotland until May.
Test strips show free Iron II ions present before and absent after treatment
Watermark after application of cyclododecane