By Pat Kelley, Vice President
Imagine that you have just laid out several thousand dollars for a beautiful Louis XV style Grandiose Desk, ornate with bronze decorations, leather top, and made with high quality ebonized wood with the typical Boulle 17th Century inlaid brass. Now imagine that you are finding small conical piles of sawdust on the floor beneath several of the corners. What is your next step? It is always good to start with the insect first. With wood boring beetles, it is best to locate which pieces of wood are affected, determine if it is an active infestation and then identify the species. This information is crucial for determining your next action. With higher valued materials like antiques and other historic pieces, it is also extremely important to take into account the types of materials that are part of the piece. This particular desk has wood, leather, brass and bronze components. Each separate component can have adverse reactions to fumigant gasses or other forms of treatment. The trend in museums over the past decades has been to freeze first. Freezing is generally accepted as one of the friendliest forms of treatment to both the applicator and the artifact. But with the case of our very large desk, it would be difficult to find a freezer big enough to place it in. There are only a limited amount of other accepted treatment options for these highly valuable objects.
Let’s discuss each below:
Anoxia: A target of less than 0.3% oxygen over a 3 week period is needed to achieve a kill. This can be achieved using nitrogen gas or argon gas to flush out the oxygen to this extremely low level. For large items such as furniture, a barrier film that includes foil, polyethylene, and Mylar is commonly used to seal off the item. The procedure can also be done inside a fumigation bubble. Standard polyethylene alone is insufficient to keep oxygen levels low enough. This treatment requires quite a bit of effort and daily monitoring of the oxygen levels.
CO2: When using CO2, we typically shoot for a concentration of 80% for at least 14 days at a temperature of 77 degrees F. CO2 increases the respiration rate of insects. With CO2 we see an increase in the breathing rate; we see a loss of energy as the oxygen level drops; we see a loss of water in the insect and eventual dehydration and we also see both CO2 poisoning and suffocation of the insect. The use of a fumigation bubble or permanent CO2 chamber is necessary to contain this very active gas molecule. A humidifier will also be needed to keep the RH levels high enough to prevent damage from desiccation to the furniture.
Phosphine: If there is any metal incorporated into the furniture, this is not the 5method to use. Phosphine can be extremely corrosive to copper and copper alloys such as brass. If the antique item that you want to fumigate is wood and wood only, phosphine can be a very effective gas to use. Simply tarp the furniture in a 4 ml or thicker polyethylene in a safe location. Then, let it sit for 3 days or more at room temperature with the prescribed dosage for that volume of space. The penetrating gas will find its way to the insects that have burrowed deep within the wood.
Sulfuryl Fluoride: Sulfuryl fluoride is typically a nice fumigant to use on most antiques. While pure SF does not cause any corrosion to metals, the small amount of impurities that come in the cylinders of sulfuryl fluoride can cause slight corrosion to some metals, but at a much lesser rate than phosphine corrosion. Care must be taken with the shipment and application using these high-pressured cylinders of gas. The monitoring equipment to correctly use this fumigant gas is also relatively expensive.
A great piece of advice when treating antiques is: “know what material components are incorporated into each and every object. Select a treatment option that will kill the insects but not damage the antique. Make sure that whoever owns the object being treated agrees with your choice of treatment prior to starting the treatment. Finally, plan in advance for every aspect of your treatment so you don’t get any unpleasant surprises.”
This King George XV desk has wood, leather, brass and bronze components. Each separate component can have adverse reactions to fumigant gasses or other forms of treatment.