I feel pretty accomplished this week! Allison and I fixed the Raman on Monday by basically turning it off and on again (no joke – although there was some flailing involved) and from there I was able to handle the Book of Hours for the first time this summer. It became apparent very quickly that I will encounter many logistical obstacles when taking spectra, including which pages I am able to analyze due to the limitations of the height of the stage. Allison did come up with a fun little solution to at least part of this, though, by laying a clean slide on top of a page and then using small weights to gently hold it down far enough so that the pigment comes into focus.
The first two days that I spent with the manuscript were basically a whole lot of fumbling around and not a ton of finding actual, distinguishable peaks on the spectrum. Thursday, however, I read a paper by Lauwers et al that was able to put many things in perspective for me. Namely, that the pigment we suspect is there – azurite – is anisotropic. This means that the spectrum is strongly orientation-dependent and therefore requires particular positions that can really only be found by frequently changing which crystal I’m blasting with the laser. The paper also gave me a link to a fantastic source on which Raman peaks to expect for certain pigments called Non-destructive microanalysis of cultural heritage materials by Vandenabeele et al. A lifesaver, truly.
With these things in mind, I made sure to try and take spectra of crystals with different orientations and expand my selections from only dark blues to sky blues and even whites. The logic behind this is that azurite under the microscope isn’t uniform in color and can range from white to deep blue. I also discovered by playing around (very tentatively, carefully, and slowly) that 10% power was not harmful to the pigment (no photobleaching), and so with all of these developments I was able to actually take a few decent spectra that look a whole lot like azurite. WOO!
They’re all shifted slightly below the expected values, but because it’s consistent we’re slightly optimistic. I’m hoping that further data collection will help support this, as it did today when I looked at the blues in the Calendar instead of just the Hours of the Virgin. I’m also hoping to learn more about mapping which was introduced to me on Thursday and which may prove very useful in the future.
So, goals achieved: Took spectra of the manuscript! Kind of matched these to literature values!
Goals not achieved: None!
Next week: Do some work on a purple-ish letter on the back of page 13. It’s just below a lovely blue letter, so it’d be interesting to find out if it was a different, non-azurite blue originally which faded or if it was always supposed to be purple. This may prove difficult according to the couple spectra I took of it today, but we’ll see. I’m also planning to just get more data points at other blues throughout the text as well as learn more about mapping.