The use of lacquer (nitrocellulose) for the coating and preservation of fossil leaf compressions

Abstract

Cuticular features and details of fine venation are now widely relied upon in systematic and phylogenetic studies of fossil plants. Where fossil leaves are robust or adherent to the matrix, such features may be readily available, but should the remains be fragile and subject to damage or loss, it may be necessary to preserve their integrity immediately following recovery and during transport. Clays, shales, and fossil leaf compressions are particularly vulnerable to the drying environment; fossil specimens are commonly damaged or entirely lost due to spalling, cracking, and shrinking of the clays or due to exfoliation of the organic film caused by differential drying. In an attempt to eliminate these problems, a technique using a mixture of nitrocellulose lacquer and acetone to coat fossil leaf compressions was developed for use on freshly excavated specimens under a wide range of climatic conditions (subfreezing to warm, dry or wet) while in the field. Many other preservational techniques exist, but they are typically complex, expensive, time consuming, destructive, or were developed for use in a laboratory setting.

Leaf compressions from the Late Miocene sections of NW Italy: research on an efficient, easy and quick consolidation treatment

“…commercially available under the trade name of Vinavil ® ) have been used to repair fractures or as a support for whole pieces (Collinson 1995); they have also been applied to the leaf surface to consolidate this fragile layer on the matrix (Mastrorilli 1965, Collinson 1987. Solvent-soluble varnishes, fixatives or acrylic sprays can sometimes preserve the fossil from further degradation when already exfoliated, but it is important to guarantee the correct moisture condition in order to avoid the coating clouding phenomenon (Collinson 1987, Lepage andBasinger 1993). Unfortunately, the consolidant tends to form a shiny layer, which is disturbing from an aesthetic point of view and also hindering observation under an optical microscope.…”

“…In general application to partially or completely dried samples is pointless (Collinson 1987). Lepage and Basinger (1993) sprayed samples with a nitrocellulose lacquer diluted in acetone or in high-quality lacquer thinner, such as Lucite ® series by Dupont. This treatment produces good results, however, some nitrocellulose formulations were found to contain abnormal amounts of phenolic resins causing darkening of the coating.…”

A new method to prepare clean cuticular membrane from fossil leaves with thin and fragile cuticles

“…We first use nail polish to "strengthen" the thin and fragile cuticle, and then macerate the material in reagent(s) to obtain clean cuticular membrane which is still adhered to the thin clear nail polish film. Commercial products of colorless nail polish had long been used in cuticle preparation, both in the "transfer of cuticle" method and the "replica of cuticle" method [30,31,33], as well as in cuticle preservation [35]. But compared with other material, the results by using nail polish have been generally reported as unsatisfactory [30,31,33].…”

The resin transfer technique: An application to insect fossils in laminated limestones of the Crato Formation (Lower Cretaceous) of north-east Brazil

“…Usually, the fossil is removed completely from the matrix and is left partially embedded within the epoxy resin, although variations in its application will determine different outcomes. For example, in some techniques, the specimen is simply protected from further damage by a transparent resin coating (Holm, 1890;Lepage and Basinger, 1993). In others, the fossil is embedded in resin, then the opposite pristine surface exposed via mechanical or chemical preparation (Cridland and Williams, 1966).…”