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?