Detective Work: Investigating art
Why?? to help direct restorationto help conservationto aid interpretationjust to “know”
“Is a painting ever done?” Ball, Time as Painter, Chapter 11
Methods:1.spectroscopy (“quantify interaction with light”)2. chemical behavior ( “does it react?”)3. microscopy (“visual with a microscope”)
Transmission
Reflection
lightcolor “thrown away(observed)
Transmission and Reflection effectively do the same thing: throw away unabsorbed colors
Absorption
Absorption
“Light” is a term that refers to a electromagnetic radiation.
And electromagnetic radiation are waves of different energies that extend over a broad range:
If the electromagnetic spectrum were a piano keyboard…..
cosmic gamma X-rays UV Vis IR Radio induction power
wavelength, nm 10 -8 10 -6 10 -4 10 -2 1 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 nm
frequency, Hz 10 26 10 24 10 22 10 20 10 18 10 16 10 14 10 12 10 10 10 8 10 6 10 4 10 2 Hz
the visible spectral region would be just one key!
X-rays UV Vis IR
light source sample detector
interacts with light;“removes” (absorbs)some light components
Interaction type: electronic vibration
Observed results: none none color heat
Chromate, CrO4 2-
“chromophore” in chrome yellow
X-rays UV Vis IR
Interaction type: electronic vibration
Observed results: none none color heat
X-rayaffectsinnerElectrons:Higher energy
UV/visaffectsouterelectrons:Lower energy
X-rays UV Vis IR
Interaction type: electronic vibration
Observed results: none none color heat
where in painting: penetrates all surface below paint
wavelength selected to interact most with black of underdrawing
X-rays interactionstrength dependson number of electrons:
Pb >> Zn, Ti
Lead white scatters X-raysmore than zinc white or titanium whiteor most other pigments (except HgS or Ba-pigments)
Infrared SpectroscopyInstrumentation
An infrared spectrophotometer is composed of:1) an IR light source, 2) a sample container, 3) a prism to separate light by wavelength, 4) a detector, and a recorder (which produces the infrared spectrum).
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ir/instrumentation.html
SEE:AlizarinCarmineIndigo
begin with historical context:•when did artist/work occur•workshop/atelier context and influences?•location•information on commission/motivation for work
Feast of the Gods
An analysis by WebExhibits
Microscopy: What can you observe? Crystals? Shape: Are there faces or regular shapes or blobs?
Large or small? Homogeneous or a mixture?
Size? Pigment particles have characteristic size depending on how produced.Ground minerals are larger (and usually retain crystal morphology)Precipitated manufacture pigments are smaller (fine)High temperature processes (smalt) makes larger chunks,
Color? There’s the obvious…. What color is it?
Also, does reflected light have the same color as transmitted light?Or, is it pleichroic? (appears a different color in different orientations)
Chemical reaction?
Does it dissolve?Does it react / change with an acid? With a base?
Refractive Index: relative measure of light velocity as it passes through pigment?
Isotropy: isotropic? Anisotropic? Axial? Biaxial?