## 2 Materials and Methods
### Sample Post-Processing  
The post-processing included a total of five different technologies. The primary goal of these modifications is to slow down the degradation of the test samples by eliminating the moisture absorption of the final product. The first technology was so-called chemical smoothing using dichloromethane vapors (declared concentration min. 99%). For this purpose, a glass container with a volume of 5 l was used, which was closed with a cover glass (only by its own weight). To prevent contact of the samples with the liquid dichloromethane, the samples were suspended in the container using a glass rod. The volume of dichloromethane in the container was 0.5 l. The smoothing process took place by placing the container on the printing pad of the 3D printer at a temperature of 60 \(\pm\) 5 \({}^{\circ}\)C for 18 min (for all sample types). After that, the samples were transferred to a closed curing box with a temperature of approximately 20 \({}^{\circ}\)C and a relative humidity of approximately 50% for 3 days. The possibilities of using dichloromethane and other solvents are listed, for example, in the publication [10]. The samples were then heat treated in an annealing furnace at a temperature of 85 \(\pm\) 5 \({}^{\circ}\)C. To ensure the uniform heating, temperature resistance, and cooling of the samples, they were stored in finely ground limestone (grain size 5-10 \(\upmu\)m) in a stainless-steel tub. About 1 kg of limestone was used. The samples were always heated to an ambient temperature of 20 \({}^{\circ}\)C.  
The heating time to the annealing temperature was 50 min in the case of the samples for the tensile test and for the cupping test. The heating time of the samples for the impact strength test was set at 75 min, and in the case of the samples for the three-point bending test, it was set at 110 min. The duration at the annealing temperature was uniform at 60 min. After that, the stainless-steel tub with the samples was removed and left to cool down in the surrounding environment. The indicated annealing time and cooling method are also recommended in the publication [29]. The samples were cleaned of any adhering limestone using compressed air. The mentioned time intervals were practically verified in advance, and it was found that they are sufficient for the homogenization of the material in the entire cross-section of the samples. These two technologies, chemical cooling and annealing, represented post-processing without the additional application of coatings (\"coatless\" technology). The other three methods were already focused on the application of coating layers. The third method was specifically the application of a two-component epoxy resin in one layer (with the business name Efkoresin ART UV 100). Figure 1: Dimensions of the test samples (**a**–**d**) and the 3D printer (**e**): (**a**) For the tensile test; (**b**) For the three-point bending test; (**c**) For the impact strength test; (**d**) For the cupping test. Due to the nature of epoxy resins, a manual application was chosen using a short-bristled brush. To reduce the viscosity, the resin formulation was printed on the printing pad of a 3D printer at a temperature of 40 \({}^{\circ}\)C. At this temperature, it was also applied to samples whose temperatures were 20 \({}^{\circ}\)C. The mixing ratio was 100 wt. of resin and 30 wt. of hardener. After application, the samples were moved to a closed curing box for 3 days (conditions identical to those after the chemical smoothing). The epoxy resin mentioned is certified for direct contact with food. The samples treated in this way are therefore harmless to one's health. In the European Economic Area, this issue is specifically dealt with by Regulation No. 10/2011 on plastic materials and articles intended for contact with food [30]. The last two technologies included the application of a synthetic or water-based coating. The synthetic coating consisted of three layers (1\(\times\) base coat and 2\(\times\) top coats).