# Weakly Bonded Water in Interstitial Sites: A Source of Inaccuracy in Rehydroxylation Dating
## 3 Results  
The proposed experimental sequence, beginning with an initial TGA screening, allowed for effective qualitative discrimination between samples that were suitable for the standard procedure and those that were not. As shown in Figure 2, the TGA curves of the five samples clearly segregate the samples into two groups. Samples Brick_1 and Cer_2 underwent continuous mass loss starting at approximately 100 \({}^{\circ}\)C, with no apparent discontinuities until about 400 \({}^{\circ}\)C, thereby losing 2-3% of their weight. In contrast, sam ples Brick_2, Brick_3 and Cer_1 underwent more limited mass loss (<1%) in the 100 \({}^{\circ}\)C dehydration range, coupled with a stepped behavior in the mass-loss profile. The mass difference, \(\Delta\)m = m\({}_{2}\) \(-\) m\({}_{4}\), was interpreted as an indicator of the weakly bonded water fraction that remains after the standard low-temperature preheating (100 \({}^{\circ}\)C). This residual moisture leads to an overestimation of the sample age when using the conventional protocol. As an illustrative case, Figure 3 shows the Brick_1 data: as the preheating temperature was raised from 100 \({}^{\circ}\)C toward 300 \({}^{\circ}\)C, the normalized mass gain decreased, and the estimated ages converged toward the expected historical age. Table 2 further confirms that for the Brick_1 and Cer_2 samples, a higher preheating temperature significantly improved the accuracy of the dating process. Figure 3: (**a**) Normalized mass-gain contribution calculated for different preheating temperatures. (**b**) Estimated ages from data obtained at different preheating temperatures vs. expected age for the sample Brick_1. Figure 2: TGA curves for the five samples. The different mass losses in the 100–400 \({}^{\circ}\)C range are clearly visible. Furthermore, the reliability of rehydroxylation (RHX) dating critically depends on the complete removal of weakly bonded water. The experimental evidence presented here indicates that a standard 100 \({}^{\circ}\)C preheating is insufficient for samples with significant interstitial water retention. Our data demonstrate that raising the preheating temperature to around 300 \({}^{\circ}\)C effectively clears these water molecules, thereby yielding more accurate dating results. In addition, the kinetic parameters extracted from the mass-gain curves, especially the growth rate \(\alpha\) as a function of temperature, support the hypothesis that the rehydroxylation process follows an Arrhenius-like behavior. The linear regression of the ln\(\alpha\)(T) versus T\({}^{-1}\) plot (Figure 1b) not only confirms the temperature dependence but also facilitates the determination of the activation energy for the RHX process. A critical examination of previous work in this field reveals both similarities and improvements in our approach. [PERSON] et al. [5; 7] originally established that the mass gain in ceramic samples follows a t\({}^{A}\) power law, attributing this behavior to the slow kinetics of hydroxyl incorporation after initial rapid water absorption adsorption. While their work laid the foundation for RHX dating, subsequent studies (e.g., [10; 20]) raised concerns regarding the reproducibility and the influence of incomplete dehydration on dating accuracy. Our study addresses these concerns by incorporating an initial TGA step to identify water-fraction retention and by systematically varying the preheating temperature. The observed improvement in dating accuracy, particularly in samples Brick_1 and Cer_2, demonstrates that tailoring the preheating conditions (up to 300 \({}^{\circ}\)C) can mitigate the overestimation error. Moreover, while [PERSON] et al. [12] reported variability in water-release behavior among different ceramics, our comparative analysis shows that a carefully controlled preheating protocol can standardize the dehydration process across heterogeneous samples. Additionally, our results are consistent with the broader literature, which underlines the importance of mineralogical composition in RHX kinetics [16; 17].