Posts Tagged ‘chelation’

Since last August, I have been pursuing an informal treatment study on batches of Civil War-era documents undergoing washing and deacidification.  Today, I’d like to share some informal, preliminary results.  First, a very cursory overview of some relevant conservation chemistry.

Paper inscribed with iron gall ink, like these Civil War documents, frequently undergoes two types of degradation.  One type is caused by the presence of acid in the paper.  The second type is caused by the presence of iron ions in the ink.  Both types of degradation weaken paper, causing it to discolor, become brittle, and break.

Washing and deacidification treatments address the first problem by neutralizing pH and adding alkaline buffer.  In recent years, chelation treatments have been developed to address the second problem.  These treatments lock up iron ions and make them unable to continue damaging paper. 

I frequently pursue washing and deacidification in the TSLAC lab, and I have been considering introducing a chelation workflow, as well.  To help make that decision, I decided to evaluate the effectiveness of my current treatment by measuring acidity and iron ion presence in the Civil War documents before and after treatment.  Surface pH is measured with an Extech handheld pH meter, and iron ion presence is evaluated with iron gall test papers developed by the ICN conservation program in the Netherlands.  I classify the test paper results from 0 (no iron ions indicated) to 4 (iron ions strongly indicated.)

Given published research, I expected that washing and deacidification would affect paper pH strongly, but would have a negligible impact on iron ion levels.  My preliminary results are surprising.  Average pH increase was more modest than expected: it changed from 4.40 before treatment to 5.56 after, for an average change of 1.16.  Average reduction in iron ion presence was more pronounced than expected:  rankings changed from 1.7 before treatment to 0.4 after, for an average change of -1.3.  Not only does the after-treatment paper remain surprisingly acidic, but it also shows a surprisingly marked reduction in iron ions given that chelation was not pursued. 

These results are very informal, and testing continues monthly.  Myriad explanations can be imagined, not least including inaccuracies inherent in surface pH measurements.  (The unsuitability of destructive sampling is a frequent challenge in conservation research.)  Perhaps additional baths are needed to improve pH.  Perhaps without chelation, the iron ions become more diffuse during washing, creating risks less localized but more pervasive.  I’d be very curious to hear other conservators’ thoughts and interpretations as I consider future washing, deacidification, and chelation treatments.

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