213 Large reptiles, localised solutions: investigating alternative delivery systems for the treatment of oversized pyritic specimens by Lucia Petrera 1 , Lu Allington-Jones 1,2 , and Kieran Miles 1 1 Natural History Museum, London, SW7 5BD; 2 l.allington-jones@nhm.ac.uk Received 27 February 2020. Accepted 26 April 2020. Ethanolamine thioglycolate and sepiolite paste is a traditional method for localised treatment of pyrite oxidation products, but there are drawbacks to the technique. Te paste can be difcult to apply, especially on non-horizontal surfaces, and is occasionally inefective. Tis article documents trials of solvent gel delivery systems and proposes Laponite RD (a synthetic colloidal clay) as an efective alternative. Petrera, L., Allington-Jones, L. and Miles, K. 2020. Large reptiles, localised solutions: investigat- ing alternative delivery systems for the treatment of oversized pyritic specimens. Geological Cura- tor 11 (3): 213-216. Introduction Pyrite in its pure form and as a constituent of fossils and mineral specimens is a common component of earth science collections and is inherently unstable in our atmosphere: pyrite will oxidise in the pres- ence of moisture. Te by-products of this reaction usually comprise sulphur dioxide, sulphuric acid, and hydrated ferrous sulphates (Miles 2019). Tese decay products are a health hazard and will lead to acidic corrosion of other minerals, labels, and stor- age media. Expansion cracks may also occur because the oxidation products, and their hydrates, are much larger in volume than the original minerals (Larkin 2011). If lef unchecked, pyrite oxidation can destroy specimens and their labels. To prevent continued deterioration, oxygen and relative humidity levels must be controlled (Alling- ton-Jones and Traford 2017), but this is not always possible for oversized specimens such as entire ma- rine reptile specimens in slabs (a small detail of such a specimen is shown in Figure 1). Ammonia vapour treatment of the oxidation products (Irving 2001) is benefcial, but again problematic with large spec- imens (Andrew 1999). Te alternative is localised treatment with ethanolamine thioglycolate paste (Cornish and Doyle 1984). Tis method will not prevent future oxidation, but it stabilises the decay products, removing harmful mineral hydrates from the surface and reducing susceptibility to damage at the standard relative humidity for museum galleries and storerooms that contain mixed collections. Ethanolamine thioglycolate and sepiolite (a natural clay) paste has been used for decades to treat large specimens with active pyrite oxidation (Cornish and Doyle 1984; Fenlon and Petrera 2019) but it is dif- cult to apply on non-horizontal surfaces, due to its tendency to crumble. With developments in solvent gels for cleaning water-sensitive objects (Stavroudis 2017), it became time to explore alternative delivery methods. Figure 1. Archive image of active pyrite oxidation in the stomach area of a plesiosaur at the Natural History Museum in London (UK). A gel is a liquid formulation thickened with a poly- mer or other high molecular weight material. Gelled formulations are used to lengthen solvent retention time and to control the depth of penetration by limiting capillary action. Tis occurs because the solvents are held within the gel and will not evapo- rate or spread as rapidly as unconstrained solutions. Tey are also used to control the cleaning process on vertical or other complex surfaces or to increase the gel’s efectiveness in extracting the soiling or stain as the gel dries. Te advantages of gels include control of solvent evaporation rate and of capillary fow into