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Aufarbeitung einer historischen Nass-Sammlung – Ein Arbeitsbericht über die Behandlung von alten Nasspräparaten

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Abstract

The article presents a detailed guide to the processing of historical wet collections, exemplified by a fish collection. Exhibition as well as conservation aspects are discussed. Different methods are presented and illustrated for each work step. Furthermore it is focussed on the processing of dried out specimens, as well as an up-to-date and very effcient sealing method for jars using a light vacuum. (This article is published in german)

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... The original Steinmann fish collection consisted of a total of 1,012 jars and other receptacles. The inventory showed that 56% of the jars contained well-preserved specimens, but the rest were in need of reconditioning (Neisskenwirth 2019). Of the total of 450 jars that needed reconditioning, 70 jars contained numerous specimens that had completely dried out. ...
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Different procedures are proposed in the literature for the rehydration of dried-out specimens. These procedures vary greatly in their efficiency and application. This work describes a new procedure that is inspired by the literature but that avoids heating the specimens. This method was applied to reconditioning dried-out specimens from a historical collection (Swiss freshwater fishes, bird brains, and bird eyes), stored at the Naturhistorisches Museum Bern in Switzerland. The procedure consists of five steps. The first step is the softening of hardened soft tissue with benzaldehyde and demineralized water. The second step is an indirect rehydration with water vapor. The third step is a chemically induced direct hydration using a trisodium phosphate solution that allows the specimen to swell in size before being washed with water to remove all additives. Finally, the rehydrated specimen is transferred into new preserving fluid. Because the dehydrating properties of ethanol as a preservative are problematic, this paper presents the results of an experimental case study using a glycerol solution as a preservation fluid.
Chapter
2.9.1 Microslides Microslides are relatively easy to store and may be kept at room temperature under normal conditions. Slides should be handled gently, kept in the dark and at cool temperatures, and stored on stable shelving, especially in the case of large and heavy slide collections (Carter and Walker 1999). Permanent mounts are best prepared with resin-based products, such as Canada balsam and Euparal for botanical and mycological specimens, (Carter and Walker 1999) and epoxy resins for fossils. As slide mounts will always remain fluid to some extent, they should be stored flat with the mount on the upper side. Slotted slide boxes, for instance, should be stored upright like books on a shelf and marked in a way that indicates how to open the box correctly, to prevent slides from falling out and breaking. Microslides may be stored together with the main collection or separately with other microslides. Fossil microslides In fossils, the size of the microslide should correspond to the nature of the fossil, whether it be a longitudinal or tangential cut or a cross section, a small or large fossil, or a cross-drilling sample from a large fossil (e.g. Chinsamy and Raath 1992, Stein and Sander 2009). Commonly used microscope slides for fossils, also referred to as palaeohistological slides, come in different sizes: common formats are 2.5 × 5 cm, 5 × 5 cm, 7.5 x 5 cm. Unusual formats may include anything up to self-cut window panes measuring tens of centimetres in length and width. Palaeohistological slides are usually thicker than standard microscopy slides used in biology labs. They can be up to several millimetres thick, partly to withstand strains on the slide that might occur during the preparation of the fossilised samples. Due to the wide range of sizes and thicknesses, palaeohistological slides are stored in a variety of different slide boxes. Labels for microslides Care must be taken with slide labels. Some commercially available slide labels are unsuitable for permanent preparations because of the poor quality of the paper or glue. If a self-adhesive label is used, ensure that it is of archival quality (with acid-free adhesives) (Carter and Walker 1999). Recommendations à standardise storage types if possible à use resin-based mounting for long-term storage, i.e. Canada balsam and Euparal in botanical and mycological preparations, and epoxy resins infossil preparations Examples to see one of the largest collections of palaeohistological slides in Switzerland, visit the PIM in Zürich to see preserved microscopic algae (diatoms) on microslides and stored in histologic preparation boxes, see the MHNG in Geneva for taxonomic studies, the type specimens represented in the cryptogamic collection of the CJBG in Geneva have been removed from the general collection and stored in separate fire-proof metal cabinets (Clerc et al. 2017) Supplier storage boxes can be bought from a broad range of histology lab suppliers like Carl Roth Laborbedarf (Arlesheim CH, www.carlroth.com/ch) Further reading for an extensive overview of storing, managing, and digitizing slide collections see Neuhaus et al. (2017)
Chapter
Fossils can be completely petrified, include original material or organic matter, contain unstable mineral parts or belong to the so-called subfossils consisting mostly of original material. The latter often do not differ significantly from zoological objects and can usually be stored in the same way (see section 2.7). Completely petrified fossils are the least problematic and may be stored relatively easily under standard conditions, like simple hard rock specimens and most other stable minerals. Fossils with unstable components may require special rooms or storage conditions. Small, fragile fossils may need to be stored in closed containers, boxes, or glass vials to prevent specimens and labels from getting lost. Even in smaller fossils, the application of accession numbers directly onto the specimen can prevent misplacement if several containers or storage boxes are opened for comparative studies or for inventory purposes (see figure 2.8.4.a). Pyritised fossils are unstable Pyritised fossils, containing the iron sulphides pyrite or marcasite, are unstable and prone to decay under normal atmospheric conditions, a process known as ‘pyrite-mar - casite destabilisation’ or ‘pyrite disease’ (Larkin 2011). The combination of high relative humidity and atmos - pheric oxygen causes a reaction producing sulphuric acid that attacks affected specimens and which may also affect nearby drawers, labels, boxes and other neighbouring fossils. If stored in glass, affected specimens can expand and shatter their containers. Decay can be prevented if specimens are stored in an oxygen-free environment, i.e. in an inert gas compartment. For larger specimens or whole collections, however, this may not be feasible, given the costs associated with airtight storage cases or other such storage options. According to Larkin (2011), the neutralisation of sulphuric acid may be achieved through treatment with ammonium gas or ethanolamine thioglycolate. Important prevention measures include the identification and isolation of potentially affected pyritised fossils, a rel- ative humidity between 30 – 45% if possible but certainly below 60% and regular collection checks to detect the beginnings of pyrite decay, such as the presence of greyish-yellow dust smelling of sulphur. Oil shale fossils can easily fall apart Oil shale fossils can fragment if the mother rock is drying out. A short-term transfer into distilled water can save the rock from dehydration. If stored for a longer time in water (not recommended but potentially necessary in certain cases), an additive should be used to prevent the growth of mould. For mid- to long-term rescue, specimens can be stored in glycerine or permanently transferred to synthet- ic resins. In the latter technique, known as the ‘transfer method’, the synthetic resin becomes the new support for the fossil and the original, fragile sediment is removed. To perform this transfer, different 2-component epoxy resins are available, some of which are also transparent, such as Araldite, Biresin and Bakelite/Epikote. Embedding the fossil is a permanent measure. The application of transparent or non-transparent resin should therefore be care - fully considered prior to the start of preparation, and depends on the following questions: which side should be visible at the end? Should the backside of the fossil be still visible through the resin? Shall the specimen be dis- played in the future? Will indirect lighting of the fossil through the resin be used?
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