A naturally occurring resin, distilled from the bark of Abies balsomea (the balsam fir) and other N. American Abies species, which, when heated to 160 °C, becomes liquid and is used to cement mineral or rock chips to glass slides as part of the process of preparing thin sections. Its use has been largely superseded by warm- or cold-setting epoxy resins which combine low viscosity (about 100 centipoise) with high shear strength (about 11.7 × 106 Pa), good adhesion, and a refractive index of 1.54.