# Characterization of Grape Extract-Colored SiO2 Synthesized via the Sol-Gel Method
## 3 Results and Discussion
### Color Analysis of the Synthesized Hybrids  
The colorimetric analysis in the CIELAB space offers a robust method to assess chromatic differences between pure SiO\({}_{2}\) glass samples (S) and those doped with grape extract  
Figure 2: Color changing of GRE extract during sol–gel synthesis.  
(S5 GRE and S15 GRE). All the parameter results, as well as the sample images, are reported in Table 1. The L* parameter, which is 66.09 \(\pm\) 2.38 for the pure silica matrix, decreases as the grape extract content increases, reaching a value of 39.32 \(\pm\) 1.85 in S15 GRE, reflecting the material's increased opacity and reduced light transmittance. The positive values observed in the hybrid materials indicate a shift towards the red region of the color space, as opposed to green. Similarly, the positive b* values suggest that both S5 GRE and S15 GRE shift towards yellow, whereas the negative b* value for the pure SiO\({}_{2}\) sample indicates a subtle blue component in the glass. The chroma C* parameter shows a higher value compared to that of the SiO\({}_{2}\) reference, consistent with the increase in color saturation. However, S15 GRE exhibits lower saturation levels than those of the hybrid with lower extract concentrations. This may be attributed to the internal scattering phenomena. A higher concentration of grape extract could introduce more defects or microstructures within the glass matrix, increasing internal light diffusion. This scattering disperses the light less directionally, leading to less saturated and less defined colors. The h* (hue angle) values indicate the position of the color in the chromatic plane (a*, b*) and are measured in degrees, ranging from 0\({}^{\circ}\) to 360\({}^{\circ}\). The significant reduction in hue angle with increasing grape extract concentration suggests a shift in the chromatic profile. The S5 GRE hybrid, with a hue angle of 58.50\({}^{\circ}\)\(\pm\) 0.48, is closer to the yellow region of the chromatic plane, whereas the S15 GRE hybrid, with a hue angle of 30.75\({}^{\circ}\)\(\pm\) 1.44, moves towards the red region, approaching the perception of pure red [31; 32]. Based on the CIELAB analysis results, the potential behavior of these glass materials in filtering visible light can be hypothesized. Indeed, the positive a* values for both hybrids suggest that these glasses may transmit more light in the red wavelength range, as the higher a* values indicate a red-shifted color perception. This latter result is even higher for the S15 GRE hybrid, as can be observed by the higher \(\Delta\)E value, which represents the color difference in CIELAB space between the sample and the reference [33] reported in Table 1. Similarly, the positive b* component indicates that S5 GRE (with a b* value of 13.63 \(\pm\) 2.07) may transmit more light in the yellow wavelength range. This hypothetically suggests that S5 GRE could reduce blue light transmission relative to that of other wavelengths. Nonetheless, this remains a hypothesis, as total reflectance UV analysis is required to accurately determine the capability of these materials to filter specific wavelengths across the light spectrum.