Raman analysis of Garland of Howth banner

Pigment Analysis – The Garland of Howth

In the past weeks the Garland of Howth (MS 56) has returned to centre stage, this time for careful examination with Raman lasers. This is one of two non-invasive analytic techniques we have available in the conservation department; we will report on the second, x-ray fluorescence spectroscopy (XRF), in the coming weeks.

We are using this type of analysis because it can be safely used in-situ to determine which pigments have been used in making the Garland of Howth.  The procedure, called micro-Raman spectroscopy, uses lasers of specific wavelengths to excite the molecular bonds in the material. The energy returned to the detectors provides a fingerprint of the constituents under the beam.

Fig. 1 HORIBA Jobin Yvon LabRAM Raman microscope analyzing pigment in the Garland of Howth.
Fig. 1 HORIBA Jobin Yvon LabRAM Raman microscope analyzing pigment in the Garland of Howth.

The equipment we are using is a bench-top HORIBA Jobin Yvon LabRAM Raman microscope (fig.1).  It is fitted with a superhead containing an objective lens that magnifies material to 50 times its actual size, which enables us to select pigment particles of interest.  The superhead also includes a digital camera to allow visual focusing and monitoring of the examination sites during the analyses. Our laser is a red HeNe laser  which produces light energy at 632.8nm and is typically used for this type of pigment study. The beam of light is approximately half a millimetre in diameter which is essential when working on fine details in the manuscript.

This is very similar to the set-up we used to examine the Book of Kells (MS 58), 1 and is the same system we used to examine the Book of Durrow (MS 57), and the Book of Armagh (MS 52).2

We have just examined the two decorated pages on the Garland of Howth. Folio 1r contains the opening words of Matthew 1:18 and folio 22r, the beginning of Mark’s Gospel. These both show the use of a very simple palette, which includes white, red, yellow, blue in several hues, and a warm black-brown.

Fig. 2a Woad plant. Source.
Fig. 2a Woad plant. Source.
Fig. 2b Indigo pigment. Source.
Fig. 2b Indigo pigment. Source.

So far we have been able to confirm that the blue on the manuscript is an indigo pigment, most likely extracted from the leaves of the woad plant (Isatis tinctoria) which was known to be farmed in Ireland in the early medieval period (fig. 2a-b).3

Fig. 3a Orpiment mineral. Source.
Fig. 3a Orpiment mineral. Source.
Fig. 3b Orpiment pigment. Source.
Fig. 3b Orpiment pigment. Source.

The yellow is orpiment, a poisonous arsenic sulphide mineral pigment (fig. 3a-b). Orpiment readily reveals itself with Raman spectroscopy and even in areas with just a hint of yellow we were able to detect its presence.   The white, red and brown-black have yet to reveal their secrets, so will be put to the test with our XRF.

Susie Bioletti, Keeper of Preservation and Conservation

Footnotes

  1. S. Bioletti, R. Leahy, J. Fields, B. Meehan, W. Blau, ‘The examination of the Book of Kells using micro-Raman spectroscopy,’ J. Raman Spectrosc., 40 (2009), 1043.
  2. L.Burgio, S. Bioletti, B. Meehan, ‘Non-destructive in situ analysis of three early medieval manuscripts from Trinity College Dublin (Codex Usserianus Primus, Book of Durrow, Book of Armagh)’ in J. Hawkes (ed.), Making Histories: Proceedings of the sixth International Conference on Insular Art, (Shaun Tyas, Donington, 2013).
  3.  Fergus Kelly, Early Irish Farming: A study based on the law-texts of the 7th and 8th centuries AD (Dublin, 1998).