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: 1.spectroscopy (“quantify interaction with light”) 2.chemical behavior ( “does it react?”) 3. microscopy (“visual with a microscope”)

light sourcesampledetector The Basics of Spectroscopy:

Transmission Reflection light color “thrown away (observed) Transmission and Reflection effectively do the same thing: throw away unabsorbed colors 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 nm frequency, Hz Hz the visible spectral region would be just one key!

X-rays UV Vis IR light sourcesampledetector interacts with light; “removes” (absorbs) some light components Interaction type: electronic vibration Observed results: none none color heat Chromate, CrO 4 2- “chromophore” in chrome yellow

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

X-rays UV Vis IR Interaction type: electronic vibration Observed results: none none color heat where in painting: penetrates all surfacebelow 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)

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

Infrared Spectroscopy – compare two red dyes Alizarin Carmine

Carmine CochinealCochineal

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?