Silica gel cassettes are ideally suited for stabilizing relative humidity inside museum display cases.
Silica gel is the safest way to control moisture inside museum display cases
Experts know that controlling relative humidity is the key to achieving optimal conservation.
The majority of museums face two significant challenges;
The first is the impossibility of controlling the relative humidity in a room.
The second is to obtain the relative humidity requirement for specific items that are different from what is required for the rest of the collection.
To overcome these obstacles, using silica gel is strongly recommended.
Silica gel for a museum collection
Different types of moisture sorbents exist on the market, but few are targeted for the heritage preservation field.
The best known and used is silica gel, due to its high absorption capacity, its chemical inertness, and its ability to undergo an indefinite number of moisture cycles.
It’s the same silica gel found in our new clothes, leather handbags, and shoes. Very practical, silica gel is a sorbent well known to museum curators.
To gain this control, newer establishments often have central heating, ventilation and an air conditioning system.
Those systems allow uniformity of relative humidity for a room or a museum as a whole. However, they are usually reserved for permanent exhibitions and, are expensive.
In small establishments, active systems such as humidifiers and commercial dehumidifiers are used.
For most museums, the use of silica gel is the practical solution for controlling the relative humidity at an affordable cost.
Discreet and personalized
Silica gel is usually concealed in a container located at the base of the showcase. One or more openings allow the circulation of air between the base and the upper part.
Zone Display Cases is a leader in the design and manufacture of high-quality showcase displays. We know the importance of silica gel inside shop windows.
For this reason, we take care to design “invisible” showcases to incorporate them in a discreet and personalized way.
Silica gel is usually concealed in a container located at the base of the showcase.
Relative humidity is a standard measure of the moisture in a specified environment (outside, in a room or a display case). Technically, RH is the ratio of the amount of water vapor in the air to the maximum amount of water which the air can hold at a given temperature, expressed as a percentage.
RH can also be defined as the ratio of the actual water vapor pressure to the vapor pressure saturation.
Why control relative humidity?
Each artifact has its own relative humidity needs.
In other words, each object in the collection will act differently according to its attributes. The relative humidity ranges from 0 to 100%. Too low humidity is at a rate of less than 35%. The air is moderately humid between 35 and 65%, and beyond, the atmosphere is humid.
Within the same space, the RH varies according to the temperature changes: it increases if the temperature decreases and decreases if it rises.
The dangers of too low relative humidity
Dry air becomes problematic when it comes into contact with organic objects, such as paints, wooden furniture, books covered with leather. As a result, they may lose flexibility and crack.
However, too low humidity will not affect preserved metal objects.
The dangers of too high relative humidity
Mold formation is, without question, the most significant risk when there is too much moisture.
This biological danger is always to be avoided since it causes irreversible and often catastrophic damage.
The value that is generally recommended to prevent the growth of mold is 65%. Below the threshold, no mold can form, whatever the temperature.
The dangers of significant variations in relative humidity.
In addition to the risks associated with very wet or arid environments, abrupt variation can lead to the deterioration of collections.
If you want to change the environment of an object, it is important to acclimate the object, slowly, to avoid the risk of crack formation.
Organic materials, of plant or animal origin, tend to equilibrate depending on the humidity of the environment.
They adjust to changes in humidity in the air by absorbing and desorbing water vapor. Among the most vulnerable objects are panel paintings, inlaid objects, papers, and animal skins.
Objects impregnated with salt, such as some metals and ceramics, are subject to damage caused by changes in relative humidity. When the salt changes from the liquid state to the solid state, its volume becomes more massive. The object is therefore under stress and may suffer damage.
Although it is impossible to prevent changes in relative humidity, it is essential to slow down this process as much as possible.
- Jean Tétrault et Paul Bégin, « Gel de silice: Contrôle passif de l’humidité relative – Bulletin technique 33. » Gouvernement du Canada, Bulletins techniques de l’Institut canadien de conservation (ICC). (En Ligne) https://www.canada.ca/fr/institut-conservation/services/publications-conservation-preservation/bulletins-techniques/gel-silice-humidite-relative.html(Page consultée le 10 décembre 2018)
- André Bergeron et Colette Naud, 1995 (Révision 2011), « L’humidité relative et la température ». Centre de conservation du Québec, Conservation préventive dans les musées, (En Ligne) http://www.ccq.gouv.qc.ca/index.php?id=171 (Page consultée le 10 décembre 2018)