Thomas Jefferson’s change to the Declaration of Independence

Published on July 5th, 2010 | by Admin

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subjects

Spectral imaging of an ink smudge on the Declaration of Independence shows that Thomas Jefferson covered over the word “subjects” with “citizens”.

About 80 years ago, some archivist sandwiched the pages of Jefferson’s draft between sheets of plastic. When the document was taken out of its permanent display case for a brief analysis last year, Library of Congress research scientist Fenella France noticed an uncharacteristic smudge.

France had been probing the document with a new tool known as hyperspectral analysis. It uses LEDs, or light emitting diodes, to successively illuminate an object in 13 discrete bands of light; they run from the ultraviolet through the visible spectrum, and into the infrared. A 39-megapixel camera records the object under each type of light.

Right away, France says, she noticed that under the different spectral bands the smudged segment of the document changed, suggesting that the top word — citizens — might be hiding something. For the longest time, she said, “I didn’t know what it was” because the two inks were very similar. Jefferson carefully wrote over the bottom word to camouflage it, she says. All she could initially see were tiny regions sticking out from below, including a “t” towards the end.

Various pigments, inks and paper treatments will respond differently to some wavelengths of light. The camera “gave us a series of images that we could [digitally] stack, kind of like a deck of cards,” France explains. Software scouted for variations in the image under each spectral band. France then assigned a false color to the elements that differed most so that they would emerge against the background.

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3 Responses to Thomas Jefferson’s change to the Declaration of Independence

  1. Roger Easton says:

    It was spectral “IMAGING” and not spectral “analysis” that produced the result. In the latter, the spectra of the different features are measured to determine the chemical constituents. In the former, digital images are collected under different wavebands of light and different weighted sums of those bands are evaluated with the goal of creating images that enhance the features being sought.

  2. Thanks Roger, I’ve edited the post to reflect this.

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