Background: Color change in artworks has been commented on for centuries. Fading of watercolor pigments is a notable alteration. Pigments based on carminic acid are among those particularly prone to color loss, but the mechanism and factors are not well understood.
Results:We painted out three pigments prepared from the aqueous extract of carminic acid (CA) from Dactylopius coccus: the uncomplexed, and aluminium-and tin-complexed lakes. These were applied in a 2% gum Arabic solution to papers that were acidic, neutral or alkaline pH and exposed to accelerated light aging in a weatherometer. The comparative rate of fading was dependent on the complexation and on the pH of the substrate. On alkaline paper, the Al complex was least light stable, on neutral paper the three colorants responded similarly, and on acidic paper the tin complex was the least light stable. This is discussed in light of the published information on reactions and mechanism of color loss of CA.
On January 26, 2011, the Pardon of Patrick Murphy, a document in the U.S. National Archives and Records Administration (NARA) Record Group 153 (RG 153) Records of the Office of the Judge Advocate General (Army), was submitted to conservation for examination. The record was examined with special focus on the handwritten “1865” to the left of Abraham Lincoln's signature. All analysis techniques were non-sampling, non-invasive, and non-damaging as retaining the integrity of cultural heritage is very similar to the forensic handling of evidence. Microscopy, transmitted light, Ultraviolet-induced visible fluorescence, and X-Ray Fluorescence (XRF) spectroscopy analysis confirmed that the ink used to write the “5”, in the April 14, 1865 date is different from the remaining text written by Lincoln and these analytical forensic-inspired techniques allowed scientists and conservators to “set the record straight” about the modern forged “5” for future generations of researchers.
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