Curatorial practices of museums, such as coating bivalve shells in paraffin wax, risk contaminating the stable isotope values (e.g., δ13C, δ15N) of subsequently analyzed periostracum (the outermost, proteinaceous shell layer). Using shells of two species (Lampsilis siliquoidea, Obliquaria reflexa), we evaluated the impacts to periostracum δ13C and δ15N values of paraffin coating and removal using three experiments. First, we tested for isotopic shifts associated with coating the shells using a paraffin-xylene solution as well as exposure to a xylene-only solution. Using gas chromatography-mass spectrometry (GC-MS), we also evaluated the efficacy of removing paraffin using five consecutive rinses in a xylene solution. As part of this evaluation, we calculated the proportion of hydrocarbons (paraffin wax) removed after each rinse and measured periostracum δ13C and δ15N from both paraffin-coated and coated-and-removed periostracum samples. All isotopic analyses were conducted in the Stable Isotope Laboratory at the University of Cincinnati. Bivalve specimens came from the Zoological Collections of the Cincinnati Museum Center. We conducted each of the three experiments using five specimens of each of the two target species. From each specimen, we collected three replicate samples for both untreated (control) and treated conditions. For some of the paraffin removal experiments, final replicate numbers per individual fell to one or two due to loss of periostracum during the xylene rinses. For each replicate sample, we report δ13C, δ15N, %C, and %N values. For each individual shell, we also report mean, median, minimum, maximum, and range of δ13C, %C, δ15N, and %N values.