The Chemistry of the Book of Kells

The Book of Kells is a spectacularly illuminated gospel manuscript dating from around 800AD and held in Trinity College library in Dublin. Some idea of the colours achieved can be seen below. 

I thought it would be of interest to list how these colours were achieved.

1. Black ink was made from oak-galls mixed with iron sulfate and acetic acid from wine or vinegar. Carbon-black ink was used less frequently
2. Greens made by mixing arsenic sulfide and indigo (extracted from the Woad plant) or using verdigris, which is a copper carbonate or chloride.
3. Red dots were made from red lead, or Pb₃O₄.
4. Blue used indigo, not lapis lazuli.
5. White was gypsum or calcium sulfate.
6. Yellow was arsenic sulfide, known as auripigmentum since it had a lustrous golden quality.
7. Purple came from a lichen (Roccella tinctoria) which is better known to chemists as a source of litmus; the basic chromophore of which is 7-hydroxyphenoxazone.

If you ever visit Dublin, do go and see the manuscript for yourself.