Works of Art & Antique Humidification
One of the most important and basic factors in the preservation of art collections is the stability of the surriunding environment, requiring temperature and humidity to be strictly controlled.
Fluctuations in temperature and humidity caused by external factors, I.e.heating, sudden weather changes, an in-flux of visitors, etc, are a major problem for museums. In particular fluctuations that occur repeatedly over a period of a few hours or days will have the most damaging effect as the materials do not have enough time to acclimatise. For example, an influx of people at one time will increase the humidity considerably, especially on a rainy day.
These effects may be very visible such as materials warping, splitting or cracking or they can be micro-scopic but over time will become more obvious. As works of art grow older they become brittle and fragile, and less able to readjust their internal moisture level without damage.
Museums need to control the environment around exhibits 24 hours a day, seven days a week as temper-ature and relative humidity can fluctuate frequently and dramatically on a daily basis. This requires con-stant operation of the humidification system, which therefore needs to be reliable.
For many institutions the fundamental design parameters for relative humidity is between 45% and 55% throughout the year, allowing seasonal fluctuations between the two extremes, but holding daily fluctua-tions tn +-3C.
Any humidification system installed must be to react quickly to a drop in humidity, shut down rapidly when the humidity level is increased and modulate from 0-100% operation to cope with the close control required.
Effects of dry air on art, antiques and museum exhibits
Paintings_Made up from several layers, each individual layer reacts to moisture loss in different ways causing them to blister and the paint layer to flake off. Canvas painting are considered less susceptible to gradual long-term fluctuations, but rapid fluctuations may damage the canvas or paint layer.
Paper and papyrus_Although moisture can be put back info these materials they have dried out, a constant hydrating and dehydrating cycle is not good for the paper structure and can cause damage.
Woods_The amount of damage that will be sustained will be dependent on how the wood was primarily seasoned. Older woods that have not benn dried out using modern kiln techniques will have a moisture content of around 12-15%. If these woods are stored in a centrally heated environment, this may lead to cracking and movement of joints. More severe damage will be caused to veneered surfaces. Warping can also occur when the external layer loses moisture whilst Internal layers do not, causing them to detach themselves or become loose.
Ivory_Hygroscopic changes may lead to thin elements of the structure cracking. Even a draught from a window may be enough to cause irreversible damage.
Textiles_Often these materials are stretched across wooden boards or frames, causing a restriction in movement when they are handled below their natural moisture level. Silk is particulary at risk as are exhibits that contain hair.
Pottery, terracotta & stone_Will have their internal mineral content altered in most or dry conditions. Salts that are in the substance will rise to the surface when wet and then crystallize when dry, This can lead to stains on the surface, powdering and flaking.