I started working on cultural heritage science with a bench-top Horiba Jobin Yvon Raman Spectrometer in 1999. I did keep working on other Raman systems from time to time. A lot has been written on this technique and its applications for Art and Archaeology.So, this post just provides — as usual — my personal insights.
An affordable Raman system
There are plenty of systems for Raman spectroscopy. I’m interested to mobile solutions which can be used for on site examination. Among the “mobile” systems there are some that are pretty heavy; the spectrometer and power laser are hosted in a luggage — such the one I worked with for the Leonardo’s project for the Battle of Anghiari in 2010.
For on site art examination we need a mobile and lightweight. I worked with the DeltaNu Inspector 785. This is a very low cost Raman system, probably the cheaper, and really light. I tested it on my collection of historical pigments painted with gum Arabic. So, basically this is the case if you plan to work on manuscripts. I got acceptable Raman spectra from the pigments listed below (a “Y” means a characterizing Raman spectrum could be acquired).
red ochre Y
Red lead Y
Yellow ochre Y
Cobalt yellow Y
Cobalt green Y
Cadmium green Y
Phtalo green Y
Chrome green Y
Cobalt blue Y
Ultramarine natural Y
Phtalo blue Y
Ultramarine synth Y
Van dyke brown
Vine black Y
Lead white Y
Lead Tin yellow Y
titanium white Y
When it comes to oil painting the instrument performance is much worse. I didn’t try the system on oil painted test swatches but on an old oil painting. I could see peaks just from the strongest Raman scatterers; vermilion and lead white. The linseed oil fluorescence is really strong even if with the 785 nm laser in the DeltaNu Raman Inspector.
This system can get Raman Spectra until 2000 cm^-1. Prussian blue has its strongest emission at 2154 cm^-1, so, unfortunately this system misses to identify this important pigment.
References on Raman Spectroscopy for Art
This topic has been extensively covered by a number of publications. You can find many on the internet.
My PhD Thesis on Raman Spectroscopy for Art. Unfortunately, it’s just in Italian and it’s a bit outdated, 2004.
Raman Microscopy in art and Archaeology If you never heard about Raman Spectroscopy for art this is a nice introductory paper. H.G. M Edwards,Spectroscopy 17(2) 2002
Free Software for Raman Spectroscopy
Most Raman spectra are in the .spc format. You can use a very simple and free software to open them from Thermo Scientific SPC Viewer.
If you want something more flexible and yet free try out Spekwin32. So far the best free Raman software. I noticed that on Win7 you have to run it as administrator otherwise it doesn’t load the spc files.
Database of Raman spectra for Art
- ColoRaman. It’s still online, the Raman spectra database of pigments I develop for my PhD. You can still look at it to see how the Raman scattering changes with 3 different laser wavelengths.
- e-VISART. Run by Dr Kepa Kastro, useful collection of spectra with peaks intensity noted.
- University of Parma. This is a Raman database of minerals but since most pigments are minerals…This project springs from the passion of Dr. Danilo Bersani for minerals’ collection.
- Romanian Database. While writing this post I checked out this website and had the pleasure to discover this group has develop a nice program, RDSS. I actually do the same thing in order to interpret a Raman spectrum. I made an Access MS Database with, for each art material, a column for the main peak, another column for the second intense peak and so on.. Then, other columns for reference papers, pictures of the spectra, notes,.. I’ll keep using my Access DB but I will compare my data with theirs. Nice program.
- RRUFF. University of Arizona runs this outstanding database. it’s pretty unique because you can download the spc file so you can compare - using a software such as Spekwin32 - your spectra with these standards.
- UCL. This is a classic you cannot miss. Prof. R.J.H. Clark — University College London –has played a pivotal role in the development of Raman microscopy for art and this is one of the first database ever made on this topic. You can also download the spc file. Useful, clean, simple.