## 1 Introduction  
The presence of soluble salts in porous cultural heritage materials can cause significant decay through crystallisation or hydration cycles upon interaction with the environment and fluctuating relative humidity (RH) and temperature [1; 2; 3; 4; 5; 6]. The exact RH and temperature ranges that can cause issues depend on the salt mix present. Quantitative analysis of the salt ions present is required to assess this. When these conditions are met, the extent of damage depends on the amount of salt present. In many instances, low concentrations of salts engender apparent stability of an object. If this variability in response can be predicted from analysis, decisions can be made about which objects and situations require environmental control. Providing this control can be expensive and have a negative impact on sustainability. The standard analytical approach at present is to drill a sample from the object [7]. The diameter of sample needed depends on the grain size, with larger grain sizes requiring larger samples to be representative. Samples are generally taken to at least 2 cm in depth, with the surface 1-2 mm discarded. The samples are dried, weighed, extracted with high-purity water, filtered and analysed with ion chromatography. The results can be used with thermodynamic modelling to determine the temperature and RH regions within which pressure is generated by that particular salt mixture [8]. This has proved an effective strategy to design preventive conservation strategies to minimise salt damage [9; 10; 11; 12], although the detailed behaviour of some species mixes remains unclear [13]. While an effective approach, drilling a sample is clearly undesirable, and two alternative methods have been investigated; complicating the surface to extract a salt sample and combined non-invasive analysis with a microwave moisture meter and dielectric capacitance meter. The microwave moisture meter is unaffected by the presence of soluble salts in the water in the object, whilst the dielectric capacitance is significantly changed from that of pure water. A number of parameters of each method were investigated. There is an enormous body of work investigating politicting to remove soluble salts from stone and other porous media. The understanding of mechanisms has developed greatly, and new poultice media are being developed [14; 15; 16]. However, this is often not fully quantitative and generally focusses on how much salt is removed, not whether the salt removed through poulticing is representative of that in the body of the object. Unsuccessful extraction from wall paintings has been reported using poultices [17]. At present, no non-invasive method exists to determine salt species concentrations inside porous media. The SUSI@ equipment uses dielectrics and can map water content and a parameter labelled as the salinity index, which is related to conductivity of the salt solution, but does not identify the individual salts [18]. Hyperspectral imaging in the far infrared (1100-2500 nm) has shown promise with sample salts [19], but its applicability to all common salt mixtures has not been determined, nor its information depth. This means drilling will have to be continued as a sampling method. The investigated method, if successful, could be used to prioritise which objects to drill. Also, if a mapping method can be found, this will be valuable in deciding the most representative areas to take samples from. Mixed salts (acetate/formate with chloride/nitrate) can be formed via reaction with soluble salts in the porous media and carboxylic acids in the environment (especially in enclosures) [20; 21; 22]. Their presence is an important indication that the environment requires mediation to reduce the carboxylic acid concentration. Traditional analysis with X-ray diffraction (XRD) can be complicated through lack of standard patterns and is relatively slow. In-situ analysis with direct reflection FTIR microscopy can provide spectra of sufficient quality for identification and has a much faster workflow.