Durability of traditional and new nanoparticle based consolidating products for the treatment of archaeological stone tools: Chert artifacts from Atapuerca sites (Burgos, Spain)

The increase of durability to slowdown damage of chert artifacts is assessed after their treatment with traditional consolidating products (acrylic resin and ethyl silicate) and new products based on SiO2 and Ca(OH)(2) nanoparticles. The stability of the treatments is analyzed submitting the samples to wetting drying cycles and UV light exposure accelerated aging tests. Non-destructive techniques are used to compare the superficial consolidating efficacy, the chromatic changes and the modifications in the hydric behavior after one month from the application of the products and after the aging tests. Regarding to slowing down damage of the artifacts and the stability of the products facing aging, the mixture of nanoparticles is a non-suitable product, especially in the case of relative humidity variations, which cause the loss of the consolidating product surface layer. Color changes are also produced as a result of light exposure. This mixture could be a possible product to be used in volumetric re-integrations if its drawbacks are solved. The three other products slow down damage by enhancing the superficial cohesion of the samples. However, some differences in their efficacy and undesirable results are observed. In spite of the acrylic resin is the most frequently used by restorers, is the less stable product with the lowest consolidating efficiency and inappropriate chromatic changes after wetting-drying cycles. The ethyl silicate, even though its consolidation efficacy is kept after aging, being more stable than the resin, also suffers chromatic modifications and produces significant changes in the hydric behavior. Si02 nanoparticles are the most stable product, remaining effective after the accelerated aging tests, producing low color changes despite the modifications in the hydric behavior of the treated samples. Results show that lightning gives rise to surface damage, producing superficial decohesion that can trigger higher color changes and a rise in water vapor absorption rates due to surface disaggregation. Whereas wetting-drying cycles give rise to more internal damage leading to porous system and hydric behavior modifications of all the treated samples. (C) 2016 Elsevier Masson SAS. All rights reserved.