**2. Materials and Methods**

The materials used in the research were commercial clayey mass, composed of two clays typical of the region used by the industries of Campos dos Goytacazes, RJ, Brazil. The mass is predominantly kaolinitic and has been used in other studies [5,8,9]. Moreover, natural quartz sand and glass waste were used in the formulation's soda–calcium plan. The waste was obtained from a company located in Rio das Ostras, RJ, Brazil.

The raw materials used in the research were characterized by X-ray fluorescence (XRF), using an S2 POLAR equipment, from BRUKER supplier. In addition, they were characterized through physical particle size tests, using the procedure of NBR 7181 [20], and through scanning electron microscopy (SEM) using a Shimadzu SSX-550 Superscan equipment. The samples used in SEM were prepared in advance using sanding and polishing. The samples were tested immediately after the metallization process, not requiring a conditioning step.

The formulations were produced using 60% clay 1, 20% clay 2 and 20% natural sand, as shown in Table 1. In addition, it was proposed to replace 0–20% glass waste, as a substitute for natural sand.


**Table 1.** Formulations used for production of red ceramics.

The formulations defined in Table 1 were initially evaluated for linear and optical dilatometry using a Netzsch brand DIL 402 pc equipment with a heating rate of 5 ◦C/min and a maximum temperature of 1050 ◦C. The rate used in this assay can vary in the range of 3–5 ◦C/min (slow burning), as the dilatometry results are close and do not affect the discussion of the results [21,22]. The masses of approximately 2 g were previously sieved in a sieve with 42 µm opening and prepared with 8% moisture, for subsequent compaction in a cylindrical shape with a force of 2 tons, with an application time of 5 s. In the formulations before firing, plasticity tests were also carried out, through the Atterberg limits defined by NBR 6459 [23] and NBR 7180 [24]. In this way, it was possible to obtain the prognosis of extrusion.

Afterward, the specimens were produced by extrusion, using a prismatic geometry of 15 × 25 × 115 mm. These specimens were evaluated for linear shrinkage by drying and dry density before the calcination process. The firing was carried out in a laboratory Muffle furnace by Maitec model FL 1300, at 800, 900 and 1000 ◦C. In the burning, a heating rate of 3 ◦C/min was used until reaching the burning temperature, with a plateau of 240 min. Cooling was by natural convection. After firing, density after firing, linear retraction after firing, water absorption, and flexural strength, were all tested. The procedure was adapted from NBR 15310 [25] and NBR 15270 [26]. Finally, microstructural analysis was performed using SEM.
