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Revisiting Acryloid B-72®/Paraloid™ B-72 and Barrier Numbering: A Pilot Study and Suggested Solutions for Archaeological Museum Collections

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This report provides the final results of the collaborative study of the acrylic resin Acryloid B-72®/Paraloid™ B-72[1] for barrier coat numberings conducted by the National Park Service’s (NPS) Southeast Archeological Center (SEAC), and the Institute for the Preservation of Cultural Heritage (IPCH) at Yale University.  Methods of analysis at IPCH included impregnating samples of B-72 with water, measuring the absorption of water into the solution at different percentages of relative humidity, and examining the disruption of permanent ink with the B-72 solution.  The museum technicians at SEAC field-tested the suggested mitigations of these issues, as reported by IPCH.   SEAC evaluated higher and lower concentrations of the Paraloid B-72 and acetone solution, different brands of ink, and different instruments for marking.  The details of the tests from IPCH can be found in their final report “Investigation into causes and mitigation of defective object labels based on Acryloid/Paraloid B-72,” which is being submitted alongside this report.  The details from the testing at SEAC can be found later in this report.

Results show that the current method of marking artifacts at SEAC and the guidelines in the NPS Conserve-O-Gram need to be revised to allow for greater flexibility in different climates.  In particular, the 25% concentration of B-72 recommended by the NPS[2] is too viscous to allow for a smooth base coat of B-72 to be applied.  For a top coat, the 25% solution also does not allow for a smooth application nor does it allow the top coat to dry quickly enough to keep the catalog numbers legible after marking.  Furthermore the recommended use of Higgins® Black Magic® permanent ink for marking needs to be reconsidered in light of other inks on the market.  Recommendations to fix these issues include:

  1. Decreasing the percent concentration of B-72 to allow for a smooth application of base and top coat.
  2. Increasing the number of base and top coat applications to protect the surface of the artifact and the label.
  3. Training staff in mixing the solution and correcting viscosity as needed during labeling.
  4. Checking the ingredients/formula of permanent ink for changes over time.
  5. Testing new instruments for marking for better ink application and less potential for damaging the surface of the artifact.
  6. Regular housekeeping/checking supplies for aging or decay and discarding supplies as necessary.
  7. Better temperature and humidity control in the laboratory environment.

Finally, the report acknowledges that the analysis has limitations.  Some of these limitations include: not testing pre-made B-72 solutions from NPS recommended companies, not testing the proposed changes outside of a lab setting, not testing the thermo-plasticity of the B-72 resin, and not testing all possible additives to the solution.  This report, therefore, does not represent the final authority on the subject but provides conservative and practical suggestions for using and adapting B-72 for barrier numbering.

[1] For the sake of simplicity this will be called simply B-72 throughout the paper.

[2] Sullivan and Cumberland 1993, 1.

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