## 8 New Technologies
### Ionic Liquids  
In spite of the research to find new and sustainable materials and solutions for the restoration of CH stones, very little attention has been paid to ionic liquids (ILs). In the last two decades, this class of functional and multifunctional materials has become a \"major subject of study for modern chemistry due to their high potential of applications in many industrial fields\" [52; 53]. ILs, in brief, are low melting point organic salts which exhibit a variety of tunable properties such as low vapor pressure, high thermal and chemical stability, recyclability, good electrical conductivity, and wide electrochemical range. They are largely used as alternative \"green\" solvents for conventional organic media (VOCs) in chemical synthesis, catalysis, separation processes, biomass processing, electrochemistry, and nano- and biotechnologies [54]. The chemical versatility of ILs stems from their ionic nature, which allows a synthetic control on their physicochemical and biological properties and functions through appropriate choice of the anion/cation couple, creating theoretically infinite possibilities. By anchoring to chosen substrates such as polymer networks, silica substrates, and nanosystems, ILs based materials can be built with specific thermal properties, mechanical stability, catalytic functions, and even new functions [55; 56; 57]. The majority of ILs are based on nitrogen or phosphorus cations (imidazolium, ammonium, piperidinium, phosphonium, etc.) (Figure 5a). The anions, which usually are employed as modulating agents of overall ILs properties (hydrophobicity, viscosity, etc. ), may consist of simple halides (Cl\({}^{-}\), Br\({}^{-}\), I\({}^{-}\)), and organic and inorganic species (Figure 5b). Their widespread use has posed serious environmental concerns. Numerous studies have been carried out to establish ILs toxicity and biodegradability as functions of the cation and/or anion species [58]. The green credentials of ILs have been revised, giving rise to the so called \"ILs of third generation\" based on naturally occurring and/or biodegradable ions (for example, cholinium, morpholinium, aminoacids, drugs ions, etc. ), which may have intrinsic biological and pharmaceutical activities [59; 60; 61]. IL surface activity has gained much attention. Surface active ionic liquids (SAILs) have been proposed, among others, as an intriguing and varied source of novel ionic surfactants, with a high impact in colloidal/surface/nano-science and biotechnology [62; 63]. Due to their structural analogies with conventional amphiphilic quaternary ammonium (QACs) species, SAILs have an intense antimicrobial activity [64; 65; 66]. Their bioactivity is mainly correlated to their lipophilicity/hydrophobic behavior, with the cation playing the main role in that it is responsible for the primary electrostatic interactions with cell walls [67; 68], while the role of the anion is not fully established [69]. Biodegradability of ILs is, among others, dependent on alkyl chain length. Too short or too long C atom chains make ILs less biodegradable [58; 59; 60; 61]. By application of well-known techniques, such as polymerization, self-assembled monolayers, and so on, ILs grafted surfaces with controlled wettability, antifouling, and sensing functions have been obtained [70; 71; 72]. Figure 5: Representation of common classes of (**a**) cations and (**b**) anions, respectively, used as IL constituents. ILs were successfully applied in the CH field to clean calcium crust (CaCO\({}_{3}\), CaSO\({}_{4}\), CaC\({}_{2}\)O\({}_{4}\)) from stained glasses [73], and synthetic and natural varnishes [74]. Surfactant phosphonium ILs, based on the luminescent 8-anilino-1-naphthalenesulfonate and 1-pyrene carboxylate \"metal-coordinating anions\" (Figure 6), were tested for corrosion crust removal from medieval glasses. The results were more efficient than conventional EDTA [75].