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

amount of light (color) absorbed lots little 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 Truth Objectives for Tuesday:

light sourcesampledetector The Basics of Spectroscopy:

A =  * b * c the “ black box ” the brains for the box

amount of light (color) absorbed lots little

amount of light (color) absorbed lots little Absorption Spectrum of Blue Filter

amount of light (color) transmitted lots little Transmittance Spectrum of Blue Filter

Transmission Reflection light color “thrown away (observed) Transmission and Reflection effectively do the same thing: throw away unabsorbed colors Absorption

amount of light (color) absorbed lots little amount of light (color) transmitted lots little Transmission Spectrum Absorption Spectrum

nm Our eyes are pretty good, but not as quantitative as a spectrum from spectroscopy Example 1. Shiraz wine does look different from Chianti (!) Chianti Shiraz  wavelength

the fate of an open bottle of Shiraz: Black Swan Shiraz, fresh:Black Swan Shiraz, open 12 days: 530 nm510 nm Example 2. Shiraz does taste different when left open.

© handprint.com, 2004, Bruce MacEvoy Reflectance curve for ultramarine blue watercolor 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 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 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) IR X-rays

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

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’ mass detector magnetic field separates light and heavy mass ions Molecules in gas phase as ions + or -

Electron impact ionization

Calculated mass of mauveine C 24 H 19 N 4 = 363 g/mol 24 C = 24 x 12 = H = 19 x 1 = 19 4 N = 4 x 14 =56 = 363 Calculated mass of pseudomauveine C 26 H 23 N 4 = 391 g/mol 26 C = 26 x 12 = 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: 92 Mo, 94 Mo, 95 Mo, 96 Mo, 97 Mo, 98 Mo,