Investigating art
Why?? to help direct restorationto help conservationto aid interpretationjust to “know”
( see: “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”)
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Understand:
1. what is spectroscopy
2. how it quantifies color
3. what is meant by light absorption, reflectance, transmittance
4. how to generate a reflectance (transmittance) spectrum from an absorption spectrum and vis versa.
5. how broad spectroscopy is, e.g., how infrared spectroscopy is possible, UV.
Lab
1. Measure visible spectra of mauveine and pseudomauveine
2. Obtain Infrared spectrum of carmine and of mauve
3. Run ESI-MS on mauveine and pseudomauveine
Objectives for today:
Tickling Out the TruthObjectives for Tuesday:
light source sample detector
The Basics of Spectroscopy:
A = * b * c
the “black box”
the brains for the box
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Absorption Spectrum of Blue Filter
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Transmittance Spectrum of Blue Filter
Transmission
Reflection
lightcolor “thrown away(observed)
Transmission and Reflection effectively do the same thing: throw away unabsorbed colors
Absorption
Absorption
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TransmissionSpectrum
AbsorptionSpectrum
600 700 750 nm650550
Our eyes are pretty good, but not as quantitative as a spectrum from spectroscopy
Example 1.
Shiraz wine does look differentfrom Chianti (!)
Chianti
Shiraz
wavelength
the fate of an open bottle of Shiraz:
Black Swan Shiraz, fresh: Black Swan Shiraz, open 12 days:
530 nm 510 nm
Example 2. Shiraz does taste different when left open.
© handprint.com, 2004, Bruce MacEvoy
Reflectance curve for ultramarine blue watercolor
http://www.handprint.com/HP/WCL/color2.html#reflectance
Reflectance curve for phthalocyanine cyan
Watercolor Pigment Reflectance Curves:
How does ultramarine blue
pigment differ from
phthalocyanine blue?
© handprint.com, 2004, Bruce MacEvoy
Reflectance curve for ultramarine blue watercolor
http://www.handprint.com/HP/WCL/color2.html#reflectance
Reflectance curve for hansa yellow watercolor
Watercolor Pigment Reflectance Curves:
How does ultramarine blue
pigment differ from
A yellow pigment?
“Light” is a term that refers to 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)
IRX-rays
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
Investigating the Renaissance
a Harvard site with examples of spectroscopic methods
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
Electrospray Ionization Mass Spectrometry ESI-MS
‘black box’
massdetector
magnetic fieldseparates light and heavymass ions
Molecules in gas phase as ions + or -
Electron impact ionization
Calculated mass of mauveine C24H19N4 = 363 g/mol
24 C = 24 x 12 = 28819 H = 19 x 1 = 19 4 N = 4 x 14 = 56
= 363
Calculated mass of pseudomauveine C26H23N4 = 391 g/mol
26 C = 26 x 12 = 31223 H = 23 x 1 = 23 4 N = 4 x 14 = 56
= 391
Electrospray ionization method
makes tiny droplets Vacuum removes solvent Electric potential creates + and - ions
All Mo molecules are identified by a characteristic series of lines:
Mo isotopes: 92Mo, 94Mo, 95Mo, 96Mo, 97Mo, 98Mo,