# Recent Developments in Materials Science for the Conservation and Restoration of Historic Artifacts
## 2 Inorganic Nanomaterials in Cultural Heritage Conservation
### Case Studies  
The literature data provide several successful implementations of nanomaterials in cultural heritage conservation, illustrating their effectiveness and potential for further development. Several types of inorganic nanomaterials developed for the conservation of cultural heritage artifacts are already on the market these days. Among them, calcium hydroxide materials (i.e., Calosil(r) and Nanorestore(r)) are well known and currently used in restoration procedures. As such, in the following paragraphs, we will focus on other types of nanomaterials.  
[PERSON] et al. evaluated the effectiveness of nano-TiO\({}_{2}\) in a preservation procedure for natural stone used on the facades of a heritage building (Markovits-Matheser House in Oradea Municipality, Romania) [31]. As the results presented, the treatment of limestone surface with 2% and 5% nano-TiO\({}_{2}\) (10-30 nm, in water) led to an increase in the mechanical strength of the stone (14.57 MPa and 19.59 MPa, respectively, compared with the control samples, with values ranging from 9.36 to 9.55 MPa). At the same time, the nano-coating was observed to form a protective layer, with the nanoparticle being distributed on the surface, filling micro-cracks, interstices, and pores. According to the cited authors, the degree of nanoparticle surface coverage was 91.8%, being slightly diminished by exposure to extreme simulated climatic conditions, to approx. 88.2% [31]. As future work, the authors underline the need for long-term evaluations of the proposed solution.  
Hydroxapatite (formed in situ by the addition of diammonium hydrogen phosphate and its reaction with the calcium carbonate from the stone) was evaluated as a consolidant agent for a Hellenistic-Roman rock-cut chamber tomb at _Athienou-Malloura_ in Cyprus by [PERSON] et al. [32]. The comparative compositional and microstructural evolutions of the test areas after the addition of the phosphate and after a period of one year revealed the formation of hydroxyapatite (no significant variation between the test areas being observed) in the form of a network covering the calcite grains and increasing their cohesion. According to the cited work's findings, the treatment consolidated the friable surface of the tomb; the authors suggest as future perspectives pre-treatment of the surface with a Ca(OH)\({}_{2}\) nanoparticle solution (to suppress the calcium ions dissolution), as well as a second treatment using a saturated limewater solution and/or Ca(OH)\({}_{2}\) nanoparticle dispersions (to remove residual diammonium hydrogen phosphate).  
The use of a magnesium oxyhydroxoxide nanoparticle (5-10 nm) solution obtained by pulsed laser ablation of Mg in water for the restoration of old, low-quality paper was described by [PERSON] et al. [33]. The results, compared to a conventional treatment (using basic magnesium carbonate), revealed the effective deacidification of the paper, with the pH value reaching 7.7 (after aging, superior to the classical treatment results), compared with a starting value of 5.4. Also, the treatment increased paper whiteness (up to 10%) and strength (up to 25%). Considering the obtained results, the authors proposed as a future research direction the evaluation of the antimicrobial potential of the solution in inhibiting the growth of cellulose-digesting fungi [33].