AMBER PREPARATION FOR SCIENTIFIC STUDY: THE CASE OF ARKANSAS AMBER

Amber is the devolatilized, hardened, and fossilized version of liquid tree resin (complex mixtures of organic compounds insoluble in water). Early Middle Eocene (Lutetian) amber from the Mississippi Embayment of Arkansas (USA) is quite brittle and fragile. Greatly improved imaging of this material has been accomplished by hardening the amber in an artificial resin (Epo-Tek, Epoxy Technology, Billerica, MA). This process, which imparts rigidity to the amber, greatly increases its translucency and allows for sectioning by sealing most cracks through the embedding of individual pieces. The artificial resin is prepared by carefully mixing four parts of epoxy to one part hardener (by weight). This mixture is poured over individual samples contained in clear plastic boxes. Because of the lower density of both amber and its inclusions, such as bark, with respect to the density of the artificial resin, pieces first must be firmly glued inside the boxes with a drop of artificial resin before they are filled completely. No more than 25 ml of the artificial resin should be prepared in a container, as the exothermic mixture will begin to heat faster if prepared in larger quantities. Soon after the amber specimens are covered with the artificial resin, air bubbles contained within the amber are removed in a vacuum chamber pumped to 30 torr and the specimen is slowly dried at room temperature. The artificial resin-coated inclusions are studied with a photomicroscope equipped with an electronic image processing package, such as Auto-Montage (Syncroscopy, Frederick, MD). Out of the 338 pieces studied thus far, seven (2.1%) have arthropod inclusions (including a mite, a heteropteran, a roach, a mosquito, and a beetle) and six (1.8%) have plant inclusions (including petals and possibly moss foliage). Most pieces (93.6%) have tree bark inclusions, strongly suggesting that these amber samples represent an outer layer of resin intercalated between wood and bark. As a result of this preliminary study, a comparison with amber deposited in another major collection currently is being undertaken.