Addressing Insect Infestation in Wooden Artifacts
What do antique frames, ethnographic items, and furniture all have in common? They are made of wood and can become good places for shelter and food sources for insects. The most common culprit for wood infestation is the powderpost beetle.
Signs of an Infestation
Search atop and beneath wooden objects for “frass” – a powdery substance left by burrowing pests. Powderpost beetles bore in wood to lay eggs and - when they hatch – the grubs develop to pupae and then when mature the beetles bore out, leaving exit holes, a crisp hole with a delicate layer of frass along the perimeter.
Exit Holes - Sharp circular holes on the surface
Frass - a powdery sawdust like substance which is typically along the edges of fresh holes or settled on an adjacent surface nearby.
Insects - alive or dead on or close to the piece.
Because many antiques have historic bore marks from previous infestations, the presence of holes and frass doesn’t necessarily indicate an active infestation. When bore holes and frass are evident, it should be noted that the any movement of the piece may have dislodged historic frass causing it to become visible.
The piece should be carefully monitored for potential insect activity and the structural stability of the piece be reviewed. Typically, infestations are most evident on the unfinished sections of a piece of furniture, or frame, commonly the back panels, and undersides of a piece. The damage evident on the exterior of a piece isn’t necessarily the most concerning issue, since the infestation can significantly compromise the interior of the wood support, as well weakening of joints, and even sections of the surface can even potentially detach if the support beneath has been severely compromised.
What to do
If you find signs of active insects, immediately quarantine the infested piece from other objects by wrapping and sealing it in a plastic bag. If the infestation is localized within an antique frame, and the painting and its stretcher is not affected, the painting should be removed from the frame and the frame bagged. The painting should also be isolated and monitored as a precautionary measure.
There are a number of options to address an active infestation. Each has advantages and disadvantages depending on the piece that is exposed, and the needs of the owner.
Fumigation - Consult a specialist about options and approaches that will not affect the finish. Oftentimes this is the most expedient and cost-effective approach.
Anoxic Treatment - The artifact is placed in a special air tight bag, and the oxygen is depleted from bag. This approach is preferred and the most passive, while not exposing the piece to chemicals.
The treatment takes time to allow to deplete oxygen and takes the most time of the listed options. It is also difficult to treat large pieces, since they need to be contained with an airtight seal.
Nitrogen/Argon Gas-Oxygen is replaced with Nitrogen/Argon Gas either in sealed bag, or controlled chamber. The introduction of gas reduces the time required for treatment and does not leave a residue on the surface. It is more costly than the other options.
Freeze/Thaw - The piece is carefully wrapped, frozen and then thawed. As a proactive measure, the cycle is sometimes repeated. This treatment is expedient and does not require exposure to chemicals.
Size might become a limitation. There is also the concern that the freezing and thawing could cause expansion and contraction of the piece leading to potential splits, delamination, etc.
After treatment, and the infestation is addressed, the piece should be cleaned to remove old insect accretions and deposits. Compromised areas should be consolidated and stabilized, to ensure no further loss of the wood support, or finished surface.
There are many variables to consider when addressing an infestation. Some approaches may be detrimental to select mediums, or to components of a piece. A conservator can help determine the extent of the damage, the best approach as well as stabilize the damage after the infestation is eradicated.
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