Many times a customer will come into the shop and ask how a clock can be taken care of properly. This week we will look at the environment a clock is in and how damage can occur.TEMPERATURE AND HUMIDITY
Wood Cases - Since wood is a porous material, it readily absorbs water when humidity levels are high. This absorption of moisture causes the swelling of wood. Conversely, wood shrinks in a dry environment. The shrinkage of wood in dry environments leads to the formation of structural cracks, lifting veneer and inlays, gaps in joints and the brittle nature of adhesives. Fluctuations in humidity and temperature levels result in similar damage. While precise control of temperature and humidity is desirable, it is not always practical in homes. Therefore, damage should be minimized by avoiding extremes in temperature and humidity. This can be done by insuring that wooden clocks are kept away from heat sources such as furnace vents, fire places, warm lights and direct sunlight.
Metal Clock Cases - The greatest cause of damage to metal is corrosion. Corrosion is brought on by the presence of pollution or salts such as those present in the oil of human hands. Salts and pollution in combination with moisture can produce corrosion. When dust is allowed to accumulate on the surface of a metal object it attracts moisture thus increasing the rate at which corrosion formation occurs. Keeping metal objects clean and free of dust can reduce this problem. In general maintaining low humidity levels in areas where metal objects are stored or displayed can effectively slow down the rate of corrosion formation. The recommended temperature and humidity levels for metals are 68oF at 30% relative humidity. However, clocks that are constructed of a variety of materials such as wood, ivory or tortoiseshell should be kept under the slightly higher humidity levels recommended for wood clock cases.
Painted Metal Clock Faces - In environments where humidity levels are high, corrosion can form between the paint layer and its metal support. When corrosion develops underneath a paint layer, it can actually push the paint off the surface of the clock face. Again, the best way to prevent this damage is by providing a stable and moderate humidity level for the clock.
The recommended temperature and humidity levels for the storage and display of wooden clocks are as follows:
Temperature 70 degrees F Temperature 70-75 degrees F
Relative humidity 35%-50% Relative humidity 40-60%
Inexpensive humidity sensors can be purchased from hardware stores.
Wood finishes, stains and some paints are susceptible to darkening and fading from exposure to high light levels. For this reason painted or varnished wood clocks should be exhibited and stored in an area where bright light is not allowed to fall on them. Excessive light can also accelerate the aging and degradation of finishes resulting in a cracked, brittle and/or "alligatored" appearance. Heat generated from high light levels can also be a factor in causing damage to finishes. Some varnishes can become soft and sticky when temperatures are high. Soft finishes attract dirt easily and can become stuck to surfaces when left in contact for extended periods of time.
Carpet beetles generally subsist on protein-based materials that are often present as adhesives. Carpet beetles are generally found at joinery and inside clock cases. The presence of tiny black beetles (2mm in size), small worms or furry carcasses are an indication of infestation.
Powder post beetles characteristically bore small holes (approx. 2 mm in diameter) into wooden materials. These holes are generally the first visible evidence of infestation. Wooden objects should be routinely moved and examined for infestation. The underside of legs and drawers should be inspected since insects generally hide in inconspicuous, dark places. If evidence of infestation is found, the object should be placed in a plastic bag and isolated until it can be examined by a professional conservator.