FALVEY MEMORIAL LIBRARY

You are exploring: VU > Library > Blogs > Conserving a Giant: Resurrecting Pietro da Cortona's "Triumph of David" > Pigment Discovery with Electron Microscopy

Pigment Discovery with Electron Microscopy

  • Posted by: Kristen Watts
  • Posted Date: March 6, 2014
  • Filed Under: Chemistry

As we (slowly) move towards spring, the science team has been working on the microsample cross-sections from Triumph of David using our suite of analytical instrumentation.  As we noted in our previous entry, if a sample is going to be removed from a painting, we are going to try to get the most amount of information from it as possible. To investigate questions of pigmentation beyond the color profiles seen with bright-field microscopy, we move on to a new technique called scanning electron microscopy paired with energy-dispersive x-ray spectroscopy (SEM/EDS).

 

Photo of an SEM

Photo of a SEM

Harkening back to the science blog post describing how we use fluorescent X-rays to noninvasively image and characterize the painting, SEM/EDS utilizes a similar method to analyze pigments in our cross-sections. XRF is useful in giving us a general idea of the elemental breakdown of inorganic pigments in an area of the painting; however, because of the high penetration power of the x-rays, and the fact that it is a non-invasive characterization method, we have no way of telling whether the elements we are finding in an area is a part of the ground layer, pentimenti, or a restoration campaign. SEM is a form of microscopy in which the sample is bombarded by a high energy electron beam, which can give very precise images (up to 50,000 times magnification!) based on the collection of the scattered electrons that have bounced off the surface. We can then use these images to collect elemental maps of the layers using EDS software. EDS detects fluorescent x-rays, just like XRF instruments, but with much higher spatial precision.

 

Location of an SEM image on the overall cross-section

Location of an SEM image on the overall cross-section

The particular sample we’re discussing today was mentioned at the end of the last science blog post, taken from the red cloak of the heavily overpainted soldier on the left-hand side of the painting (see image to the left). With the enhanced magnification capability of the SEM we can get precise information concerning the inorganic materials down to the individual pigment particles. This particular SEM image, the black and white image in the photo to the left, was taken at 450x magnification, and provides a wealth of information concerning the sample.

 

 

In the main SEM image, it’s pretty clear to see that there’s at least 5 layers of paint in this one subsection. By combining this SEM image with elemental mapping data, we can see the general elemental breakdown for each of these layers. The bottom layer, with most of the calcium, silicon, potassium, and aluminum is probably some sort of clay-based ground, as seen in the image below.

Comparison of the Silicon (Si) elemental map with the main SEM image

Comparison of the Silicon (Si) elemental map with SEM/BSE image

There then appears to be a layer of vermilion (as evidenced by the presence of mercury and sulfur–HgS) before a thin layer of organic material (the thin dark layer in the SEM image) was applied, shown below.

Comparison of Mercury (Hg) elemental map with SEM/BSE image

Comparison of Mercury (Hg) elemental map with SEM/BSE image

The layers above the organic layer are where the cross-section becomes incredibly more complex, including a mixture of vermilion, aluminum-based lakes, lead white, and even some Naples yellow, as seen by the spectral evidence below.

 

An example EDS spectrum showing the presence of lead (Pb) and antimony (Sb) in one particle--indicating the presence of Naples yellow

An example EDS spectrum showing the presence of lead (Pb) and antimony (Sb) in one particle–indicating the presence of Naples yellow

As you can see, there’s a lot of information to be gleaned from such a small sample, and there is still a lot that is unknown and up for interpretation. But we’re analyzing everything piece by piece and can hopefully provide more answers in the future. Until next time!

 

10 Comments »

  1. Comment by site — May 7, 2014 @ 10:47 am

    Ces posts sοnt véritablement attractifs

  2. Comment by Jane — May 11, 2014 @ 11:33 pm

    fantastic issues altogether, you just won a new reader. What might you suggest in regards to your put up that you simply made a few days in the
    past? Any certain?

  3. Saved aѕ a favorite, I like your blog!

  4. Comment by Kasha — June 21, 2014 @ 9:52 am

    Thanks for finally talking about > Pigment Discovery with Electron Microscopy
    | < Liked it!

  5. Comment by http://bafalena.wordpress.com/ — July 13, 2014 @ 7:55 am

    Howdy! I’m at work surfing around your blog from my new iphone!
    Just wanted to say I love reading your blog and look
    forward to all your posts! Keep up the outstanding work!

  6. Comment by how to start affiliate marketing — July 19, 2014 @ 12:42 am

    Good post. I learn something totally new and challenging on blogs I stumbleupon on a daily basis.
    It will always be interesting to read through articles from other writers and practice something from their web sites.

    Feel free to visit my homepage: how to start affiliate marketing

  7. Comment by top 10 website builder — July 24, 2014 @ 4:57 am

    Hello to all, how is the whole thing, I think every one is getting more from this site, and your views are
    nice in favor of new visitors.

    Stop by my blog top 10 website builder

  8. Comment by google — August 1, 2014 @ 12:29 pm

    Hurrah, that’s what I was searching for, what a
    material! existing here at this web site, thanks admin of this site.

    Here is my web page – google

  9. Comment by credit score repair — August 11, 2014 @ 1:18 pm

    Today, I went to the beach with my kids. I found a sea shell and gave it to my 4 year old daughter and said “You can hear the ocean if you put this to your ear.” She put the shell to her ear
    and screamed. There was a hermit crab inside and it pinched her
    ear. She never wants to go back! LoL I know this is totally off topic but I had to tell someone!

    my page credit score repair

  10. Comment by casino gratis pengar utan insättning — August 18, 2014 @ 2:43 am

    It’s going to be finish of mine day, but before ending I am reading
    this enormous paragraph to increase my know-how.

RSS feed for comments on this post. TrackBack URI

Leave a comment


two + 7 =

 


Last Modified: March 6, 2014