The samples analyzed are representative of the wide range of building materials (bricks and mortars from the façade, tiles and stained glass windows) used in different parts of the building. A total of 21 samples were characterized, as can be seen in Table 1. The samples were classified into five groups corresponding to the different types of materials studied (masonry concrete, masonry mortar, brick, wall tile and stained glass). The location and the construction feature from which each sample was extracted are also indicated. In all cases, the most important materials extracted (masonry concrete, masonry mortar, brick, wall tile and stained-glass) were found, on a visual inspection, to be in a good condition, and to have a suitable size and weight for transportation and storage (specific plastic bags).

The XRD results of brick fragments (FEB5 and FWB7) from two different façades of the building (east and west) can be seen in Figure 2. The significant presence of calcite without thermal alteration suggests that brick samples FEB5 and FWB7 were fired at temperatures ≤ 750 ° C as the studies show (38), (39) (40). The presence of dolomite may be due to the raw materials used in the manufacture of the bricks, the vast majority of which come from the Paleosoils (Pleistocene) geological formation based on red clays, gravels and sands, composed of calcareous, ferruginous and dolomitic clays, together with illite minerals and lime, and dolomitic grogs (33). The presence of feldspars and muscovites was found in the geological formation and the quarries from which the raw materials used in pottery and brickmaking were extracted. In addition, the presence of analcime in the diffractogram could be due to the clay raw materials of geographical context that could contain sodium, or due to the alteration by soluble salts coming from subsoil, deposited in the bricks once laid in the building (41), (42). Another interpretation of the provenance of analcime in these bricks may be due to the addition of sodium chloride in raw bodies by brickmakers, which, as has been proved, improves its plasticity and workability, as well as reduces the sintering temperature and provides greater compaction and mechanical strength of the ceramic materials obtained (39), (43). All of this verify that the clay raw materials used are of low temperature, a fact which coincides with the geological chart of the area that indicates the presence of sediments and red clays, which chemical composition does not allow high temperature firing (33), (44).

The XRD results for mortar and concrete (FWMM3 and FNCM1) samples from the Colegio Máximo indicate that they were made from mixes based on lime-based air binder with gypsum additives (hybrid mixes), particularly in the case of the concretes. Gypsum is normally added to the mixes to ensure quicker setting, thus improving the workability of the mortars and concretes (45). The remaining components (quartz and muscovite) are local aggregates from the river. Likewise, the calcite in the sample is a result of aggregates from fragments of local marbles, limestones, dolomites and travertines found in geological sediments or river basins (River Beiro and River Genil).

Figure 2 shows also the diffractograms for the ceramic body or biscuit of the wall tiles (FWT1 and FWT2). These materials have different characteristics from those of the bricks because they must have been fired at higher temperatures of around 1000ºC, in particular in the second firing in which the thick glazes coating the tiles are melted. The XRD peaks for calcite are less frequent, suggesting greater presence of calcium oxide, which is obtained at temperatures of over 900ºC. The analcime (FWT2) may result from the decomposition of the vitreous phase of the tiles (as noted in samples from archaeological sites in Switzerland (42), (46), (47), (48), or preferably of the use of NaCl as an additive to make the body more fluid. The remaining components observed in the analysis, such as anhydrite, are typically found in local clayey soils and/or in efflorescence.

The chemical analysis of the samples (Table 2) confirms the XRD results set out above. Silicates are the main component of all the brick and tile (biscuit) samples. The mortars and concretes with a high CaO content are a binder consisting of air lime and carbonated aggregates. The presence of MgO suggests that this is lean air lime, while that of SO3 indicates that gypsum was added to the mixes to make them set more quickly. The results for the glass sample confirm that it is a “cathedral”-type soda lime glass (50) with a lead melting agent. The chromophore for this glass (light blue) has a cobalt and iron base.

The ceramic materials studied have matrixes composed of clays and tempers made of crushed rock (mixed into the base pastes) and other ceramic residues (grogs). The relative compactness of these ceramics suggests low sintering and low firing temperature. Pores of 10-20 µm can be observed. The brick fragment from the east façade (FEB5) can be seen in Figure 3 (image A). It has large pores throughout the matrix, which is based on phyllosilicates and large amounts of quartz grogs of varying size ranging from very small (250 µm) to the largest measuring around 3 mm. The laminar illite-type grogs are highlighted in red, together with the carbonate grains. The temper was hardly altered by heating, as can be seen in the quartz with well-defined, clear-cut edges. Mineralizations can be detected which coincide visually with analcime (highlighted in red). Image B of sample FWB7 from the west façade shows a ceramic material with high porosity and low compactness, with a hardly sintered clay matrix, dominated by illite grogs and schist fragments from the geological area, which range in size from 70 µm to 2 mm. A large number of unaltered quartz grogs can also be observed, marked in red in the image. Feldspar is also present as part of the clayey material from the quarry.

The mortar sample (FNCM1) from the north façade, seen in Figure 3 image C, is a very porous mortar-concrete material, with a pore size ranging from >250 µm down to micropores of ≈20 µm. The matrix is calcareous with well-carbonated lumps and fragments of aggregate of muscovite and quartz (marked in red) of between 40-50 µm in size. Image D shows sample FWMM3 from the west façade. This is an air lime mortar with a very porous matrix in which retraction fissures and isolated carbonate lumps can be observed. Acicular lumps of gypsum can also be seen, marked in red in the Figure 3 (image D).

Figure 4A (sample FNB1) shows a ceramic material with no sintering (a barely compacted clay matrix) and large quantities of pores. There are no signs of particle melting, as can be seen for example in the illite (marked in red), which has clearly defined edges with no visual signs of sintering. The EDX results confirm that ceramics are rich in illite, due to presence of magnesium, potassium and iron. In addition it can be inferred that presence of sodium is due to analcime. Image 4B (sample FEB-6) shows a ceramic material with no sintering, suggesting the use of low-temperature clay raw materials. Packages of illite without softening thermal can be observed due to the low firing temperature. The EDX analysis is coherent with calcareous and illite clays (Fe-K), fired at low temperatures and with traces of magnesium and sodium, the latter probably a consequence of the addition of plasticizers or melting agents. In both cases the results obtained are coherent with raw materials from local clay quarries in the different geological strata.

Image 4C (sample FNCM1) is a high porosity mortar concrete composed of lime and gypsum binder, and an aggregate of muscovite and probably ceramic fragments. Image 4D (sample FWMM3) is a rendering mortar. According to EDX analysis the binder is made of lime and gypsum, with siliceous and/or ceramic aggregates. The transformation-carbonatation of the air binder from Ca(OH)2 to CaCO3 is shown in red (small image).

For glazed tiles and glasses from stained glass window, the results see Figure 5A (CHT4), shows a green glazed tile. The SEM image shows that the glaze is approximately 0.20-0.25 mm thick with some fissures and microbubbles well adhered to the ceramic biscuit. A certain number of pores can be observed in the biscuit. The EDX analysis confirms the composition of a low temperature ferrous-calcareous body with potassium melting agents. The analysis of the glaze shows that it is a lead glaze which melted into the base at a temperature in the range of 900-1000ºC. Chromophore elements in the copper and iron glaze also stand out together with zinc opacifiers. Figure 5B (FWT1) shows a white tile with an approximate glaze thickness of 0.2 mm and small microbubble defects. Although the unglazed ceramic base is porous, it has an acceptable level of compactness due to the fact that the tiles were fired a second time so as to melt the glaze into the base. The EDX analysis of the ceramic base coincides with the previous sample in that it has a ferrous-calcareous type composition with potassium, typical of the raw materials from the geological area in which Colegio Máximo de Cartuja and the nearby quarries are located. The glaze (sample FWT1) is a cream-white glaze of Nasrid tradition with a lead melting agent and a tin-based opacifier-chromophore.

Figure 5C (CHSG2) shows a piece of glass with an approximate thickness of 3 mm. Dust has accumulated on the surface. The EDX analysis shows the characteristic composition of this kind of glass (a soda-lime glass with a lead melting agent).

The average results for the bricks are in line with the XRD results. All temperature values were calculated by means of the program with which the DTA/TGA graphs were processed. In these analyzes endothermic peaks can be observed in the 80-140ºC range, probably due to a loss of water which is physically adsorbed. These peaks are accompanied by a loss of weight. Subsequent endothermic peaks at 728ºC (sample FEB5) and 773ºC (sample FWB7) are due to the reaction of the calcite (CaCO3), which is very abundant in both samples. This reaction also leads to a fall in weight after which it stabilizes. The fact that this endothermic effect was registered in the analyzes of both ceramic materials indicates that the calcite was intact in both; in other words: they could have been fired at a lower temperature to that of thermal decomposition of the calcite. The graph of figure 6 indicates that the firing temperature could have been <730ºC (FEB5) and 770ºC (FWB7), respectively. This confirms the results deduced from the X-ray diffractograms. It is important to emphasize the heterogeneity of the ceramic bodies and above all the heterogeneity of the firing process, since the firing was artisanal, rather than industrial, and the manufacturers had limited technical resources at their disposal.

Table 3 sets out the average values for the bricks and mortars measured at different locations with average velocity and standard deviation data. The ceramic materials show similar values to other ceramics fired at low temperatures of ≤750ºC. Some authors report similar values for common pottery type ceramics fired at low firing temperatures at which the clay bodies do not reach sintering (38). In addition, the mortars, concretes and renders made with air lime show expected values for this kind of material (51) both in air lime mortars and in those containing gypsum additives.

The colour of the samples was also studied showing a wide palette of different tones. Figure 7 shows the chromatic coordinates L*, a* and b*, according to the CIELab1976 system (Hoffmann, 2010). The colours of the mortars, concretes and bricks from the building can be seen in image 7A. All the materials studied have a tonal position in the yellow and red quadrant except for group 2CM, which has yellow and green hints. Colorimetric heterogeneity over unpainted bricks is due to craft firing and can undergo selective oxidation reductions in kiln. The mortars and concretes have very low saturation and high levels of lightness, which results in the colour being perceived as off-white. The bricks in general are more saturated in yellow and red tones and also have high levels of lightness. The colours of the glazed area of the tiles (Figure 7B) have very heterogeneous positions in all the chromatic quadrants together with a range of lightness values, so recovering in detail the palette of colours characteristic of Granada ceramics of Nasrid tradition (52). Figure 7C displays the range of colours in the glass from the stained glass window from the Chapel of Colegio Máximo de Cartuja. In general, these are simple colours (blue, green and ochres), which are technically easy to produce.