1. Author’s Information, Intended Audience & Abstract

Author’s Information

Giovanna Di Pietro, Bern Academy of the Arts, Department of Conservation Restoration, Switzerland; Giovanna.dipietro@bfh.ch

Publishing Information

Published March 2024

Intended Audience

Bachelor or master students in conservation of cultural heritage.

Abstract

Works of art are often enclosed in closed or semi-closed cases like boxes, showcases, microclimate vitrines or especially built packages. These spaces often contain a relevant amount of hygroscopic materials. The prediction of the relative humidity response of such enclosures is based on the observation that the moisture content of the hygroscopic materials determine the RH in the surrounding volume and not vice versa. This understanding is key to developing designs aimed at stabilizing passive relative humidity changes. These lessons start with a recapitulation of the definition of relative humidity introduced as dynamic equilibrium between the gas and liquid phase of water and then explore how to predict relative humidity changes in enclosures with different characteristics: closed, semi-closed, inert and hygroscopic. The unit consists of five lessons dealing with the fundamentals of microclimate in enclosures. These lessons can be complemented with lessons for advanced students on the microclimate behind backing-board protected paintings subjected to relative humidity changes and to temperature gradients.

2. Introduction

Hypothesis

The fundamental threshold concept in these lessons is that the relative humidity in closed and semi-closed systems is determined by the moisture content of the hygroscopic materials contained in the system and not vice versa.

Conservators-restorers encounter closed and semi-closed systems containing hygroscopic materials in a number of situations. Museums’ cabinets, transport boxes, especially built packages to isolate works of art from the rest of the collection, prints and drawing in a passepartouts with a front glass pane, microclimate vitrines built within the frame of a painting and backing board protections for paintings are all examples of closed and semi-closed systems where the contained hygroscopic materials play a major role in determining the values of the internal relative humidity. Students’ conception when dealing with microclimate prediction is usually that the moisture content of the hygroscopic materials adapts to the surrounding relative humidity. This conception is rooted in daily experiences, for example in the observation of the drying processes. These lessons are conceived to introduce the idea that, as long as the system is closed and the hygroscopic materials are dominant, the moisture content of the materials will determine the relative humidity in the enclosure.

The lessons are addressed to students of conservation and restoration at the bachelor level without previous specific knowledge. My classes are composed mostly of students with different background (vocational training, high school, previous higher education) and different ages.

Major Goals and Outcomes

At the end of these lessons students are expected to be able to:

• Distinguish between systems that can be modelled as inert or as hygroscopic.
• Predict RH changes in inert systems making use of the water vapor concentration diagram.
• Predict the buffering effect of the relative humidity in closed and hygroscopic systems subjected to temperature changes making use of the sorption isotherm.
• Predict the effect of the hygroscopic materials in closed systems once hygroscopic materials are inserted into them.
• Formulate different hypothesis for the RH changes in semi-closed systems with and without hygroscopic materials.

For the advanced lessons:

• Predict which factors determine the relative humidity response of semi-closed systems like a backing board protected painting subjected to surrounding relative humidity variations
• Predict which factors determine the relative humidity response of closed systems subjected to temperature gradients.

In the lessons different didactic methods are used:

• Center teaching around big ideas:  focussing the lessons on the main concepts about microclimate that might provide overarching understanding in opposition to a detailed description of single cases;
• Use simplified systems:  presenting simple and small simplified systems like bottles with and without hygroscopic materials to perform experiments and investigate their relative humidity response;
• Observation/hypothesis/test:  asking students to formulate hypothesis for the explanation of observational experiments and to devise test experiments for their hypotheses following the Investigative Science Learning Environment (ISLE) methods of Etkina and co-workers (Etkina, 2019);
• Pre-recorded experimental results and animations:  such results function as observational experiments and avoid the time and technical difficulties of developing experiments in the classroom;
• Just-in-time mathematics:  explaining mathematical methods when and only if they are needed;
• Investigation of case studies:  in particular the use of datasheets with experimental data to be analysed and interpreted by the students;
• Peer-instruction:  asking students to discuss questions first in pairs and then in plenum (Mazur, 2014).

Finally I collaborate with my colleagues teaching in the first semester preventive conservation and a practical course called “Skill’s lab” where the aim is to introduce students who have not attended a pre-program internship to basic skills in conservation like performing a photographic and written documentation, developing short and long-term housing for different artworks, developing simple solutions for display of artworks. Within these courses students measure the microclimate within “real” systems and are asked to predict and interpret the results based on these theoretical lessons.

3. References

Padfield, Tim. www.conservationphysics.org

Etkina, Eugina, David T. Brookes, and Gorazd Planinsic . 2019. Investigative science learning environment: When learning physics mirrors doing physics. San Rafael: Morgan & Claypool Publishers.

Mazur, Eric. 2014. Peer instruction: A user’s manual. Pearson new intern. ed. Indianapolis: Pearson Education.

4. Lesson Plan

Lesson Plan (table)

Lesson Plan pdf (table) – Di Pietro

Lesson Plan (Accessible pdf) – Di Pietro

5. Power Point Presentation

Power Point Presentation

MicroclimateClosedSpaces_DiPietro [pdf]

Slides for the lessons with images (licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License)

6. Animations of Pre-Recorded Experimental Results and Excel Files of Case Studies

Animations of pre-recorded experimental results

RH in the Bottle with Water Beaker

RH Increase in a Desiccator Under Vacuum After a Beaker with Water is Inserted

RH in the Bottle with a Saturated NaCl Solution

Measured RH in a Closed System (Bottle) Initially at 30%RH, then Filled with Paper Conditioned at 65% RH and Closed

RH in Semi-Open Bottles Exposed to High RH

Animation 5. Two bottles, one containing paper (yellow line) and one empty (blue line), are initially at 30% RH and are then exposed to an environment at 80% RH. The paper absorbs moisture and leads to a milder increase of RH in the bottle.

Excel files for the case studies

CaseStudy_MicroclimaVitrine_All_Sol

CaseStudy_MicroclimaVitrine_T

7. Methods of Student Engagement

Students are engaged primarily through:

• Peer instruction, questions are in the slides.
• Group work, as detailed in the lesson plan and in the slides. Group work includes the formulation of hypothesis and test experiments.
• Analysis and interpretation of case studies, also as group work.

Basic attitude

I always begin a course with scientific data on the neuroscience of learning and the importance of making mistakes. I welcome questions of all types, there are no stupid questions, I always let students discuss in pairs or small groups and almost never directly in plenum, as students feel more validated when their opinion is shared among peers. Most important is never to undermine students and to work on their proposals, to take them seriously.