## 2 Materials and Methods
### Test Methods  
The densification degree of fired samples was studied by the determination of the water absorption (_WA_%), linear shrinkage (_LS_%) and apparent and absolute densities. Water absorption (_WA_%) was measured by the Equation (1), where, \(m_{i}\) = mass of dried specimens, \(m_{f}\) = mass of saturated specimens after boiling in distilled water for 2 h.  
\[WA\%=\frac{m_{f}-m_{i}}{m_{i}}*100. \tag{1}\]  
Linear shrinkage (_LS_%) was determined by measuring the percentage changes in the diameter of the samples. The values were calculated by Equation (2), where \(L_{g}\) = length of dried green sample; \(L_{f}\) = length of the fired sample. The determinations were performed using an electronic caliper (accuracy: \(\pm\)0.01). \[LS\%=\frac{L_{g}-L_{f}}{L_{g}}*100 \tag{2}\]  
The _LS_% and _WA_% tests were carried out on ten representative specimens and the average data was reported. The apparent density (\(D_{ap}\)) of the fired samples was analyzed by an envelope density analyzer (GeoPyc 1360, Micromerities, Norcross, GA 30093, USA) based on Archimedes principle. The use of DryFlow(r) as medium in substitution of traditional solvents or mercury is a novelty and permits to obtain a high accuracy degree [31]. The density values obtained are an average of 5 measures and the standard deviation is calculated. The absolute density (\(D_{abs}\)) was measured by gas (He) pycnometer (AccyPy1330, Micromeritic, USA), in order to calculate the total porosity values (\(P\%\)) of samples according to equation (Equation (3)). \[P\%=\frac{D_{abs}-D_{ap}}{D_{abs}}*100. \tag{3}\]  
The characteristic temperatures and sintering behavior were estimated by an optical hot stage microscope (HT Misura 3.32, Expert System Solutions, Modena, Italy) using a temperature gradient of 10 \({}^{\circ}\)C/min, Tmax = 1400 \({}^{\circ}\)C and by an optical dilatometer (Misura ODHT, Expert System Solutions, Modena, Italy) with a temperature gradient of 50 \({}^{\circ}\)C/min, Tmax = 1000 \({}^{\circ}\)C. The thermal behavior was analyzed by Thermal Differential Analysis (TG/DTA STA 429 CD, Netzsch, Selb, Germany) with the following parameters: T range = 20-1400 \({}^{\circ}\)C; AT = 20 \({}^{\circ}\)C/min, sensibility = 0.1 \(\mu\)g.  
On the fired samples a deep characterization was performed. Mineralogical analysis was carried out by X-Ray Powder Diffraction analyzer (PW 3710, Philips Research Laboratories, Netherlands) with Ni-filtered CuK\(\alpha\) radiation in 5-70\({}^{\circ}\) 20 range and speed 1\({}^{\circ}\)/min, operating at 40 mA and 40 keV. Highscore Plus software version 3.0 [32] coupled to the International Centre for Diffraction Data (ICDD) cards database were used to identify the crystalline phases. Microstructural analysis was conducted by SEM (Model XL40, Philips Research Laboratories, Eindhoven, The Netherlands) coupled with X-EDS equipment (Model QUANTAX-200, Bruker, Germany). MIP- Mercury intrusion porosimetry (Autopore IV9500, Micromerities, Norcross, GA 30093, USA) was carried out to measure pore size distributions, total pore volume, total pore surface area, etc. The measures were conducted with the following operative conditions: the equilibrium time (10 s) between pressure limits of 345 kPa and 228 MPa that permits to identify capillary pores between 0.006 and 350 \(\mu\)m.  
Elastic properties were evaluated using an instrument for non-destructive measurements based on Impulse Excitation Technique (IET) (Model Electronika MFS, Grindosonic LTD). The test highly accurate and very simple is in agreement with the ASTM 1259 testing method for dynamic elastic modulus. The calculation of Young (E), shear modulus (G) and Poisson ratio (\(\mu\)) values were performed using samples' geometric and weight data through EMOD software program [33]. Tests to evaluate the chemical resistance to acids (HCI 3 vol%) and the staining resistance (olive oil and a green pigment (Cr2O3) were conducted on three specimens for each trial following UNI EN ISO rules.