Last post I introduced a brief introduction to quinolone dyes.  Very quickly, they are organic dyes that were naturally occurring, the quinone structure absorbs and reflects light of varying wavelength (color), and the quinone structure shows a tendency to undergo a reduction reaction and lose its color.

First of all, today the portrait of Madame Valentine Clapisson looks like this:

Valentine_Clappison

As far as the scientists involved with project are concerned, I can only guess how a chemist and ceramic materials engineer team at the Chicago Art Institute (http://www.nuaccess.northwestern.edu/about-us/staff.html) got together with a chemist/biomedical engineer at Northwestern University (http://sites.weinberg.northwestern.edu/vanduyne/) and collaborated on a project to restore the colors to the Renoir painting.  On second thought, these are all essentially material scientists.  The only differences between them are their fields of study.

First of all, one of the teams developed an instrument called a SECM-TERS (for short), illustrated in this schematic

SECM-TERS

to determine individual colors and the rate of color breakdown (reference:  http://sites.weinberg.northwestern.edu/vanduyne/research/scanning-electrochemical-microscopy-tip-enhanced-raman-spectroscopy-secm-ters/).

I love the way all the data in the schematic goes into a white box labeled “computer”.   My guess is that many of the 37 people involved with this project worked on the translation algorithms in the software.  The reports do not detail how the data from the SECM-TERS was translated back to the image but the computer “output” was probably device-independent color data coordinates using something like the cieLAB color space.

LAB Colorspace Diagram

The other team would have applied the results by keying in the color data coordinates into image editing software, probably a program like photoshop…

LAB Color Picker

and apply it to Renoir’s image:

Application_to_image

to come up with this:

Valentine_Clappison_restored

A report of the effort was presented at this year’s annual meeting of the AAAS.  An abstract of the presentation can be found here:  https://aaas.confex.com/aaas/2014/webprogram/Paper11268.html.  More can be read about the process they used can be found here:  http://sites.weinberg.northwestern.edu/vanduyne/research/detecting-organic-dyestuffs-in-art-with-sers/

to be continued….