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Detective Work: Investigating art Why?? to help direct restoration to help conservation to aid interpretation just to “know” “Is a painting ever done?” Ball, Time as Painter, Chapter 11 Methods: spectroscopy (“quantify interaction with light”)

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slide1

Detective Work: Investigating art

  • Why?? to help direct restoration
      • to help conservation
      • to aid interpretation
      • just to “know”
  • “Is a painting ever done?” Ball, Time as Painter, Chapter 11
  • Methods:
      • spectroscopy (“quantify interaction with light”)
      • 2. chemical behavior ( “does it react?”)
      • 3. microscopy (“visual with a microscope”)
slide2

The Basics of Spectroscopy:

light source

sample

detector

slide3

Transmission

Absorption

light

color

“thrown away

(observed)

Reflection

Absorption

Transmission and Reflection effectively do the same thing: throw away unabsorbed colors

slide4

If the electromagnetic spectrum were a piano keyboard…..

the visible spectral region would be just one key!

“Light” is a term that refers to a electromagnetic radiation.

And electromagnetic radiation are waves of different energies that extend over a broad range:

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

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

slide5

light source

sample

detector

interacts with light;

“removes” (absorbs)

some light components

X-rays UV Vis IR

Interaction type: electronic vibration

Observed results: none none color heat

Chromate, CrO42-

“chromophore” in chrome yellow

slide6

X-rays UV Vis IR

Interaction type: electronic vibration

Observed results: none none color heat

X-ray

affects

inner

Electrons:

Higher energy

UV/vis

affects

outer

electrons:

Lower energy

slide7

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 interaction

strength depends

on number of electrons:

Pb >> Zn, Ti

Lead white scatters X-rays

more than zinc white or titanium white

or most other pigments

(except HgS or Ba-pigments)

slide8

Infrared Spectroscopy

Instrumentation

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).

SEE:

Alizarin

Carmine

Indigo

http://www.chemistry.ccsu.edu/glagovich/teaching/472/ir/instrumentation.html

slide11

Feast of the Gods

An analysis by WebExhibits

  • begin with historical context:
      • when did artist/work occur
      • workshop/atelier context and influences?
      • location
      • information on commission/motivation for work
slide12

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?

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