## 3 Results and Discussion  
### Colour  
According to the research conducted, L-FDM technology enables the incorporation of coloring substances and elements. The feasibility of dyeing the filament during the printing process was investigated, using commercially available dyes such as rhodamine B, alkali blue, methylene blue, methyl orange, eosin, fluorenone, transparent red dye from Moldoo, and black printer ink from Canon (as shown in Figures 6-9 and listed in Table 2). Initially, bar-shaped objects were printed, and then, a colorimetric and microscopic analysis was conducted to evaluate their characteristics. Further analysis was performed on the bars printed using L-FDM technology, utilizing a colorimeter and optical microscope for the structural analysis. Figure 5: Photo of the idea of the L-FDM printing system. An example using a Prusa i3 MK3S+ 3D printer and a solution of rhodamine B.  
Figure 6: L-FDM-printed colored bars. Short sample labels were placed above the bars. The photo shows polylactide bars. The first one from the left is the reference sample, while the following ones are colored samples with (from the left): alkaline blue, methylene blue, methyl orange, eosin, fluorexone, transparent red dye by Moldoo, and black printer ink by Canon. Figure 7: L-FDM-printed color cylinders of PLA dyed with: (**A**) reference sample not dyed marked ref. 2, (**B**) green dye by Ag-Bet marked 2.1, (**C**) rhodamine B marked 2.2, (**D**) transparent yellow dye by Ag-Bet marked 2.3, (**E**)avy blue fabric dye marked 2.4, (**F**) transparent blue turquoise dye by Ag-Bet marked 2.5, and (**G–L**) rhodamine B marked 2.6–2.11. Figure 8: L-FDM-printed color cylinders of PET-G (**A–I**) and ABS (**J–L**) dyed with: (**A.J**) reference samples not dyed marked ref. 3 and ref. 4, (**B–F,L**) rhodamine B marked 3.1–3.5 and 4.2, (**G**) transparent yellow dye by Ag-Bet marked 3.6, (**H**) navy blue fabric dye marked 3.7, (**E**) transparent blue turquoise dye by Ag-Bet marked 3.8, and (**K**) transparent green dye by Ag-Bet marked 4.1. Figure 9: _Cont._  
To accurately examine the color intensity of L-FDM composites, we printed cylinder-shaped objects. The design of these objects (shape and structure) allows for the observation of color spread in a single layer. For this experiment, we used PLA, as it is a transparent polymer with favorable processing parameters and minimal thermal shrinkage. Table 3 provides a summary of the assay. The L-FDM method of modification has been researched extensively, and other commonly used filaments have been tested. PET-G, which is more durable and flexible than PLA, was chosen for testing, as well as the ABS copolymer, which has a higher degree of flexibility and an opaque, matte surface. Both materials exhibit higher thermal shrinkage and require additional bed heating during the printing process. The filament dyeing process for these materials was similar to that used for PLA-based composites. Figure 8 \begin{table}
\begin{tabular}{c c} \hline
**Marking of the Sample** & **Full Sample Name/Filament and Solution Used in Printing L-FDM Samples** \\ \hline Ref. 1 & PLA reference \\
1.1 & PLA + alkaline blue dissolved in methanol \\
1.2 & PLA + methylene blue dissolved in methanol \\
1.3 & PLA + methyl orange dissolved in methanol \\
1.4 & PLA + eosin dissolved in methanol \\
1.5 & PLA + fluorescence dissolved in methanol \\
1.6 & PLA + transparent red dye by Moldoo \\
1.7 & PLA + printer ink 545 Black PIXMA 545 by CANON \\ \hline \end{tabular}
\end{table} 
Table 2: Samples presented in Figure 6 and their markings. Figure 9: L-FDM-printed color cylinders of WOODFILL (**A**,**C**,**D**,**E**) and PLA WOOD (**B**,**F**,**G**,**H**) dyed with: (**A**,**B**) reference samples not dyed marked ref. 5 and ref. 6; (**C**–**F**,**H**) rhodamine B marked 5.1–5.3, 6.1, and 6.3; and (**G**) transparent dye by Ag-Bet in order starting from the bottom: green, purple, and blue turquoise marked 6.2.