Many artists have painted over other older paintings for centuries.  That's nothing new.  Seeing the original painting without disturbing the paint of the newer painting is.  Here's the story:

http://www.sciencedaily.com/releases/2009/08/090819153917.htm

"The new instrument, called a confocal X-ray fluorescence microscope, was developed at the Cornell High Energy Synchrotron Source (CHESS) national X-ray facility. The instrument reveals minute details in hidden paintings without removing paint samples. It shoots X-ray beams into a painting and then collects fluorescent X-ray "signals" given off by the chemicals in the various paint layers. Scientists can link each signal to specific paint pigments. In addition to revealing the original image, the method is providing new information on Wyeth's materials and methods. The same technique may ultimately reveal hidden images in paintings by other famed artists, the researchers say."

The art world has to be pretty excited about this.  If this technique really comes into its own, it should be really interesting to see art museums down the road.  Will they feature exhibits of famous painters with the original painting hung right next to an X-Ray photo of what's underneath?  And will the "original" X-Ray photo produced actually hold any monetary value?  And then there's the moral dilemma of showing artwork by an artist that chose not to show that particular piece and instead painted over it.  In any event, it should be intriguing to see what comes of this new technology.

This might be interesting for a few paintings of really famous artists, but I wouldn't want to see too many of these underpaintings.  There's a reason why they were painted over and the artist felt they weren't good enough.  It is of great interest to art historians but in a way the magic of some beautiful world-renowned paintings might be brought down a notch or two. 

Hmm…on the other hand, it might be interesting to see how they did it but again, maybe just a few would suffice.  I'm really torn over this.  Should it be called "X-Ray Art"?

Nosfer said:

I just had this vision of discovering various pages with the following written (and crossed out) on them:

E = MC^5

E/2 = MC*4

E = 1/2 * MC * MC (with the word "@$#$%" scrawled in the margin)

You mean like reading Edgar Allan Poe's first rough draft of "The Raven" and finding out it was originally about a squirrel visiting him in summertime and Lenore was still alive and well?  I'd like to see the literary bobble-heads fight that one out…

Oubliette-  Maybe another way to look at it is that maybe the artist was wrong.  Maybe the painting underneath is even better, more beautiful, and more significant than the one on top.  I mean, it is a possibility.  Or that a lesser artist painted over a great one, maybe out of spite or stupidity.  But like yourself, I'm torn too.  Then again, that's always been a huge part of science…just because you can do something doesn't mean that you should.  At least in this particular case, nobody gets killed…always a plus…

I guess I've known about this since the early 80's when I had a book on infrared photography. They showed various filter's effect when photographing artwork and also went into xrays to a small degree. The longer IR wavelengths penetrate deeper, but I've never seen an example so clear as the above shorter wavelength xray images.

My sister is an artist and you can definitely see the early brush marks in IR. Fascinating stuff isn't it.