In order to preserve the internal information of paleontological fossils and give full play to their ornamental and scientific research value, it is necessary to take measures to protect fossils effectively. So far, fossil surface protection is still in the early stage of research and exploration, and there are fewer related reports, while there are more research reports on stone materials with similar structural strength and composition to fossils, and the results of the related research can provide a theoretical basis for the research and development of fossil surface protection materials. According to the different characteristics of the protective materials themselves, they can be divided into inorganic non-metallic materials and organic polymer materials. In addition, the coating process has an important influence on the protection effect, and the commonly used ones are spraying and brushing.
1.Inorganic non-metallic materials
Inorganic non-metallic materials are used for the protection of stone cultural relics with a long history, while the application on the surface of fossils is rarely reported in the literature. Calcium hydroxide, barium hydroxide are 2 more common stone reinforcement, easy to penetrate into the voids inside the stone, and then react with carbon dioxide in the air to generate insoluble substances (calcium carbonate, barium carbonate) to fill in the voids in the stone object, thus reinforcing and protecting the stone.
Although inorganic non-metallic materials are compatible with the stone, good aging resistance and inexpensive, the reinforcement of inorganic materials is mainly adsorbed on the surface of the substrate by physical precipitation, and the protective layer formed is less hydrophobic, less elastic, and weaker adsorption, and the long-term use of the inorganic material sealer will lead to serious discoloration. In addition, once the inorganic non-metallic materials are solidified, it is difficult to remove them completely, and if the performance attenuation occurs, it will not only affect the display effect of the fossil, but also will cause irreversible effects on the fossil itself, so whether calcium hydroxide and barium hydroxide can be used for fossil surface protection needs further research.
2.Organic polymer materials
Compared with inorganic non-metallic materials, organic polymer materials have better adhesion and flexibility. At present, commonly used organic coatings include nitro varnish, polyurethane coating, fluorocarbon coating and organosilicon coating. Among them, silicone coatings are regarded as the most promising materials for fossil surface protection.
2.1 Nitro Varnish
Nitro varnish, as a traditional thermoplastic solvent-based material, has been used in conservation research in vertebrate paleontology for decades. Nitrocellulose varnish is combined with the surface of fossils by physical adsorption, which has the characteristics of rapid drying, hard film, chemical resistance, etc. It is widely used in the restoration and protection of fossil surfaces in the collections of nature museums. 1993, Lepage et al. used nitrocellulose varnish mixed with acetone to coat the surfaces of plant fossils, and effectively solved the problem of peeling and cracking of fossil surfaces due to the drying of the environment. However, nitro varnish solid content is low, solvent evaporation will produce a large number of organic substances, serious pollution of the environment; construction process is more cumbersome, film durability, protection and other performance is not good. In addition, nitro varnish film has yellowing problem, which seriously affects its application in fossil surface.
2.2 Polyurethane coating
The application of environmentally friendly polyurethane coating on the surface of the stone is mainly water-based and solvent-free, of which water-based polyurethane has gradually become the mainstream direction of the development of environmentally friendly coatings due to small pollution. Waterborne polyurethane and metal ions in the stone to chemical action bonding, intermolecular force is strong, so waterborne polyurethane bonding strength is higher, while polyurethane and stone surface hydrogen bonding, thus increasing the adhesive strength and compatibility of the coating with the substrate.Hagenauer et al. used the surface sensitization method and gel permeation chromatography to study the polyurethane-based coating material as a sandstone protective agent in the Hagenauer et al. used surface sensitization and gel permeation chromatography to study the polyurethane-based coating material as a sandstone protector, and the polyurethane coating showed good durability after artificial weathering in an environmental simulation chamber, with chemical decay occurring in only 4 mm thickness of the surface layer.Xu et al. prepared a waterborne polyurethane-acrylate coating, and the prepared waterborne polyurethane-acrylates UV-cured coating has good surface sealing properties and has good application prospects in stone surface protection.
The waterborne polyurethane is characterized by fast drying speed, high degree of transparency, good flexibility, and excellent water and solvent resistance. In addition, waterborne polyurethane dispersion also has a relatively wide particle size, more stable nature, and can be mixed with a variety of other resin modification, to further enhance its performance and reduce costs.
2.3 Fluorocarbon Coatings
Fluorocarbon polymers are endowed with excellent weathering, heat and corrosion resistance as well as unique electrical properties due to their high C-F bonding energy and very stable molecular structure. In the applied research, Contardi et al. used 5% fluoropolymer to protect the limestone structure of ancient buildings, and Toniolo et al. used organofluorine polymers as the protective material on marble, and achieved good reinforcement effect. He Ling et al. selected a series of fluorine-branched acrylic acid for the protection study of marble and limestone, and found that the hydrophobicity and UV resistance of marble and limestone surfaces increased after treatment with fluorinated copolymers. In the modification study, Zhao Qiang et al. synthesized fluorine-containing and silicone-containing polymer materials through modification, and performed performance analysis tests on stone samples, thus obtaining fluorine-containing coatings with good sealing effect. Duan Hongyu et al. used nano TiO2 to modify fluorosilicone sealers, and the results of dispersion experiments and infrared spectroscopy tests showed that the nano TiO2 modification could improve the UV resistance and weathering resistance of fluorocarbon sealer coatings. If the fluorocarbon polymer is applied to the surface protection of fossils, the color, transparency and storage stability of the polymer need to be further improved.
2.4 Organic silicon coating
Silicone-based protective materials have many excellent chemical properties, such as temperature resistance, chemical resistance, corrosion resistance. At the same time, because of its polymerization product structure of the Si-O-Si bond is very similar to the chemical bonding of silica matrix sandstone, is considered to be a promising fossil protection materials. Currently, alkoxysilane monomers and organopolysiloxanes are the most widely used silicone coatings. After hydrolysis and condensation, silane monomer can be hydrolyzed and condensed to obtain cross-linked silicone polymers with organic groups in the side chain, which can be firmly adsorbed on the surface of fossils after condensing with the hydroxyl groups on the surface of fossils to form a chemical bond (Si-O-Si). In addition, silane molecules can be used as a "bridge" to the surface characteristics of the fossil group modification, increase the hydrophobicity of the surface, reduce the surface energy, is not conducive to corrosive media (such as H2O, suspended particles, etc.) deposition, which can extend the weathering time of the fossil and thus effectively protect the fossil.


Room termperature curing polysilazane, pls check IOTA 9150, IOTA 9150A. 
High termperature curing polysilazane, pls check IOTA 9108, IOTA 9118.