The Structural Conservation of Panel Paintings

Probably there is no construction that suffers more seriously as a result of the

movement ofwood than the paint on a painted panel.

—. . , 

I

   or during transit, it is crucial to

control continuously the moisture content ofhumidity-sensitive

objects such as wood, fabric, and paper.

The use of microclimate boxes to protect vulnerable panel paint-

ings is, therefore, not a new phenomenon of the past two or three decades.

Rather, it has been a concern for conservators and curators to protect

these objects of art at home and in transit since the end of the nineteenth

century. The increased number oftraveling exhibitions in recent years has

heightened the need to protect paintings during circulation (Thomson

1961; Mecklenburg 1991).

Departures from the usual climatological surroundings may cause

swelling or shrinkage of a panel, resulting in cracks, splits, and cleavage of

the support or between the support and image layers (Stolow 1967). Early

research in packing has covered some aspects that are used as criteria for

the microclimate boxes (Stolow 1965, 1966, 1967).^1 Although there may

not be an “ideal” relative humidity (RH) for museums, it is evident that

some objects require, or would benefit from, separate microenvironments,

regardless of the chosen RH set point (Erhard and Mecklenburg 1994).

The use and design of microclimate boxes have been evolving since

1892. These boxes may be divided into three broad groups: those using an
      active buffer material to stabilize the internal RH, a more recent box con-
      taining no added buffer material, and, in recent times, boxes with an altered
      gas content. Another concern is the appearance (aesthetics) of the box.

The cross-grain instability of wood has been a perennial problem to arti-

sans as it is in the nature of wood and wooden objects to seek an equilib-

rium between internal moisture content and that of the surrounding

atmosphere (Fig. 1a, b) (Buck 1961).^2

Examination of the hygroscopic behavior of various wood species

shows that green as well as old wood responds to changes in humidity

(Buck 1952, 1962).^3 The swelling and shrinkage oftwo panels was

Wood as a Hygroscopic

Material

497

Jørgen Wadum

Microclimate Boxes for Panel Paintings