**4. Conclusions**

The hygrothermal response of a passive microclimate frame hosting a portrait on cardboard by Sorolla was investigated by analyzing its internal T and RH conditions in response to the surrounding room environment. Its behavior was monitored in two different sites, i.e., the Pio V Museum of Valencia (Museum), with temperatures kept almost stable during the year, and a residential building (Private) in the same area, with a heating system active only in winter. The microclimate frame (MF) proved to be highly effective in controlling the internal RH levels but to be strongly influenced by the boundary thermal variability of the room. The ASHRAE classification of climate quality for conservation pointed out that the hygrothermal conditions in both Museum and Private would have prevented the painting only from the risk of dampness (Class D). On the contrary, within the microclimate frame, since the most dangerous seasonal RH cycles and short-term RH fluctuations were filtered out, the internal MF conditions were found to be compatible with ASHRAE Class B in Private and with ASHRAE Class AA in Museum, ensuring the best possible protection for the artifact. Moreover, the risk of chemical degradation for cellulose was assessed through the Lifetime Multiplier index, which confirmed that the microclimate frame is capable of better mitigating the risks in environments where temperature levels are adequate for conservation (Museum).

To extend our analysis to the application of the microclimate frame in the future, this study showed an example of how the indoor climate can be simulated in unconditioned buildings. In view of the climate ENSEMBLES-A1B scenario for the period 2041–2070 in the area of Valencia, this approach provided insight of the future hygrothermal conditions in Private. Even if the outdoor climate scenario is likely to be beneficial to the conservation of paper indoors in autumn, an increased risk of cellulose degradation would probably be observed during spring. The adoption of passive microclimate frames in the future expected conditions indoors would thus be an effective preventive conservation measure but it is ye<sup>t</sup> important to be aware that these passive enclosures may not be sufficient to fully avoid the chemical degradation risk if an additional mitigation of the unsuitable temperatures is not provided. Considerable improvements on the current and future indoor climate might be provided by implementing some beneficial practices in the managemen<sup>t</sup> of the environment. For example, the windows' opening might be rescheduled in order to enhance natural ventilation and a cooling device might be helpful to reduce the summer temperature peaks. In addition, passive retrofit intervention on the building envelope may be considered in order to relieve the expected effects of the climate change scenario in a sustainable manner. Notwithstanding the fact that the microclimate frames do not affect the user experience in terms of their overall dimensions and appearance, the adoption of these devices should imply that the ordinary managemen<sup>t</sup> is adjusted according to their specific features. Indeed, large temperature fluctuations in the surrounding space may cause the absorption/release of considerable amounts of moisture by the buffering agent, determining the possibility of moisture exchanges with the painting itself. This means that it is fundamental to be aware of the effect over moisture exchanges exerted by temperature, which is not controlled within these passive enclosures. Moreover, since buffers are susceptible to ageing and loss of their buffering properties, it is fundamental to recondition and/or replace them on a regular basis in order to preserve their effectiveness.

**Author Contributions:** All authors helped to develop the manuscript. Conceptualization, Formal analysis and Writing—original draft, E.V. and F.F.; Supervision, Writing—review and editing, A.M.S.; and Resources and Data curation F.-J.G.-D.

**Funding:** This project received funding from the European Union's Horizon 2020 research and innovation programme under gran<sup>t</sup> agreemen<sup>t</sup> No. 814624. This research was partially supported by the Plan Nacionalde I+D, Comisión Interministerial de Ciencia y Tecnología (FEDER-CICYT) under project HAR2013-47895-C2-1-P.

**Acknowledgments:** The authors thank CollectionCare for the funds for the publication, the Museum Pio V of Valencia, the staff of the IVACOR and the owners of the paintings. E.V. thanks Sapienza Università di Roma for the internship mobility grant.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role neither in the design of the study, in the collection, analyses, or interpretation of data, nor in the writing of the manuscript or in the decision to publish the results.
