Investigating art Why?? to help direct restoration to help conservation to aid interpretation just...

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,