Keep it together: An evaluation of the tensile strengths of three select adhesives used in fossil preparation

Abstract

Abstract The tensile strength of a select group of common fossil adhesives (50% w/w Paraloid B-72 in acetone, Paleobond PB100, and Devcon 2-Ton epoxy) was tested over a period of 9 months. Because the testing process is destructive, the tests needed to be standardized to draw valid conclusions, and because large sample sizes were desired for the most statistically accurate results, limestone adherends were used as a proxy for real fossil specimens. Paraloid B-72 in acetone at 50% w/w demonstrated long solvent retention and took several months to attain full strength. Although it was the statistically weakest of the three adhesives, it still required a significantly large force to be exerted (275.56 lbs/in2; 19.37 kg/cm2) in order for it to fail after only 3 days. If fossil specimens joined with Paraloid B-72 are provided with appropriate archival support, then the adhesive will slowly attain full strength. Devcon 2-Ton epoxy was stronger than the limestone adherends and created minor or major substrate failure in the majority of samples, indicating that its use be restricted only to specific situations, such as heavy specimens that cannot be supported externally. Paleobond PB100 samples failed on average between 535 and 636 lbs/in2 (37.6 and 44.7 kg/cm2) and generally demonstrated adhesive failure, with some minor substrate damage. Paraloid B-72 demonstrated substantial tensile strength in this study and has excellent long-term stability and reversibility. Therefore, Paraloid B-72 should be considered the default adhesive in the majority of fossil preparation practices.

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