## 3 Results and Discussion
Depending on the position in space of any affected color during the calibration process, its distance from its projected reference value will be of different magnitude and orientation depending on its initial position, closer or farther away from the state of the white value in the chart in the moment the calibration is performed. This is extensible to any other reference color in the chart. This irregular variability of the reference color depending on degradation and time explains the fluctuating results when calibrating. Aside of that, it is also remarkable to see how, even when performing a calibration with deteriorated color charts, the results presented here are of a higher quality than other similarly oriented cultural heritage conservation works with ideal charts [14]. Whilst state-of art accepted CIEDE2000 differences exceed the minimal perceivable difference threshold with an ideal chart, our physically printed charts on every material among the tested ones under a chromatic deviation equivalent to 4 years still depict values inferior to \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Hour** & **Stripe 1** & **Stripe 2** & **Stripe 3** & **Stripe 4** & **Stripe 5** & **Stripe 6** & **Stripe 7** \\ \hline
2 h & 0.356 & 0.0864 & 0.0 & 1.662 & 0.510 & 0.0 & 0.0 \\ \hline
4 h & 0.356 & 0.086 & 0.0 & 1.662 & 0.510 & 0.0 & 0.0 \\ \hline
6 h & 0.161 & 0.077 & 0.0 & 0.074 & 0.153 & 0.0 & 0.0 \\ \hline
24 h & 1.032 & 0.594 & 0.0 & 1.776 & 0.881 & 0.023 & 0.045 \\ \hline
48 h & 1.122 & 0.633 & 0.247 & 2.141 & 1.156 & 0.587 & 1.132 \\ \hline
72 h & 1.110 & 0.888 & 0.272 & 2.156 & 1.966 & 1.216 & 1.438 \\ \hline
96 h & 0.161 & 0.0771 & 0.0 & 0.073 & 0.153 & 0.0 & 0.0 \\ \hline
120 h & 0.122 & 0.0901 & 0.0 & 0.101 & 0.203 & 0.0 & 0.0 \\ \hline
144 h & 1.123 & 0.890 & 0.272 & 2.150 & 1.959 & 1.216 & 1.438 \\ \hline
**Mean** & **0.616** & **0.380** & **0.088** & **1.311** & **0.832** & **0.338** & **0.450** \\ \hline
**Variance** & **0.191** & **0.119** & **0.015** & **0.788** & **0.465** & **0.253** & **0.399** \\ \hline \hline \end{tabular}
\end{table} 
Table 4: CIEDE2000 differences for the seven tested calibrated color stripes for the Forex Smart. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Hour** & **Stripe 1** & **Stripe 2** & **Stripe 3** & **Stripe 4** & **Stripe 5** & **Stripe 6** & **Stripe 7** \\ \hline
2 h & 0.356 & 0.086 & 0.0 & 1.662 & 0.510 & 0.0 & 0.0 \\ \hline
4 h & 0.356 & 0.086 & 0.0 & 1.662 & 0.510 & 0.0 & 0.0 \\ \hline
6 h & 1.033 & 0.595 & 0.0 & 1.777 & 0.881 & 0.023 & 0.045 \\ \hline
24 h & 1.021 & 0.570 & 0.949 & 1.781 & 0.891 & 0.023 & 0.045 \\ \hline
48 h & 0.355 & 0.0865 & 0.0 & 1.662 & 0.510 & 0.0 & 0.0 \\ \hline
7 the threshold in all the cases, and most of them with a CIEDE2000 value between 0 and 1 after application of the calibration process. Overall, concluding from the color difference values, it can be observed that the four materials under consideration (laminated acid-free paper, acid-free paper, Forex Smart and Glasspack) are robust enough to resist the effects of chromatic degradation over a long period without incurring in errors noticeable to the human eye in the calibration process, in spite of the material degradation that still occurs, even if slight, when observing the metrics. If the selection of the material would only depend on the mathematical chromatic stability criterion, the most suitable and balanced one would be the acid-free laminated paper. Even if the differences are subtle from a numerical perspective, Glasspack would be discarded, and acid-free paper and Forex Smart would be seen as the second and third choices, respectively. Out of the performed tests, when it comes to deploying the structures. the selected materials should fulfil some basic requirements in order to be used in a museum environment. The most important one is that the material should be innocuous to the heritage assets in its environment. Many materials are known to release different pollutants that can cause degradation of sensitive materials [5; 28].