Materiality, Fragility, and Loss in the Medical Archive

Conservation in Process: A Late Medieval Herbal

The main section of MS49 is a fourteenth-century Herbal, with sixteen full-page paintings of plants. Each illustration is surrounded by descriptive texts by different hands, some of which were added after the images were completed. 

Where applied, the green pigment used for the plant leaves has seeped through the paper. For instance, the small round leaves of the burnet plant (folio 28, verso) appear on the other side of the page, and vice-versa. Based on the date of MS49, the green pigment could be verdigris or malachite. Both contain copper, a corrosive element. 

In more extreme cases, the paint has "eaten" through the paper. The leaves of the mandrake (folio 35, recto) created a tear in the page, which was patched up at an earlier date.

Identifying the exact chemical cause for the corrosion is essential to neutralizing the degradation process. Multi-spectral imaging and X-ray fluorescence (XRF) are two non-destructive imaging methods that conservators will use to identify media, including pigments, in MS49. Multi-spectral imaging uses a modified digital camera that photographs with either infrared (IR), visible, or ultraviolet (UV) light.  Areas that look the same to the naked eye can be readily distinguished under IR or UV light. XRF imaging uses X-rays to excite atoms in pigments, which in turn emit lower energy X-rays. Once measured, this data helps to map out the various elements  in an object. 

According to conservator Laura O'Brien-Miller, these imaging techniques can detect unique elements in ink, including impurities, which then help date the various parts of the volume with more certainty. Although retouching is already visible to the naked eye, scientific analysis can detect more instances and determine the extent of these retouchings. 

Imaging credit:  Richard Hark, Marie-France Lemay, and Laura O'Brien-Miller.