This talk, given in Saturday’s Health and Safety session, was a summary of a project at the Smithsonian’s National Museum of Natural History investigating the vapors that staff were exposed to when opening old storage cabinets.
Chemicals that accumulate from pest management or other treatments can be harmful to people, objects/specimens, and even storage furniture through inhalation, repeated exposure, and adsorbing or absorbing onto their surfaces. Many pesticides are particularly retained in lipids in specimens and in the wood components of storage cabinets – this has the potential to be problematic for those working with collections that were subjected to these types of treatments in the past, particularly natural history collections. The goals of the project were to detect, identify, and quantify concentrations of organic vapors in cabinets that were known to have held treated specimens, thereby being able to determine the level of risk. Entering into the project, mercury vapor was expected. Heavy metals and non-volatile particulates were not investigated, with the idea being that proper use of personal safety tools and regular cleaning with HEPA vacuums will negate their effect on humans.
Vapor data was collected via evacuated canisters using the USEPA TO-15 method, and a mercury vapor analyzer. Cabinets chosen for the survey were presumed to have not been opened recently (and some were known to have been left unopened for many years). Of the cabinets chosen, 55 held mammals, 100 held anthropological specimens, and 50 were empty but had held anthropological specimens in the past. Results
Contrary to expectations, none of the cabinets were found to have mercury vapor! However, 39 other volatile compounds were found. Thankfully, these compounds were only detected in the ppb levels, and all volatile compounds detected were well below (often 100-1000 times below) workplace exposure limits (TLV).
Data obtained was not significantly different from the empty and the filled cabinets, which suggests that empty cabinets retain some chemicals, even after long periods of time. However, measurements of volatile compounds present in storage outside of the cabinets were not taken.
Though these ranges are safe for humans, they may not be safe for collections stored within the cabinets or for the cabinets themselves. Two chemicals are of particular concern: PDB (1,4-dichlorobenzene) and naphthalene are both highly toxic and will be retained in fats and other proteinaceous materials. They also increase mobility of unsaturated fats and are likely carcinogenic. In addition, PDB may crystallize onto surfaces, leaving a reside that can be quite sticky and difficult to remove.
Due to the results of the survey, the authors have a few key recommendations for collections that may contain such chemicals:
Improve storage: Budget towards accelerated disposal of old cabinets. Do not reuse them, even with non-collection items. Re-house collections in metal cabinets, and segregate treated specimens from the rest of the collection.
Implement an integrated pest management system: This reduces the need for future treatments and can be non-toxic! Heat treatment is not recommended for pesticide-treated specimens.
Implement safe work practices and practice personal safetey measures: Wear gloves, minimize case-browsing, examine objects in a well-ventilated area.
Work towards remediation: place scavengers in cabinets that can’t be evaluated or dealt with now.
Mónica’s talk focused on the treatment of five oil paintings on meta at the National Center for Conservation and Restoration (Centro Nacional de Conservación y Restauración, or CNCR) in Santiago, Chile.
In 2012 five paintings from the Bernardo O’Higgins House Museum in Talca, Chile were brought to the CNCR in serious need of treatment. The paintings represented an exciting moment for the CNCR, since paintings on metal had not been treated there previously. One of the paintings was signed by Willem Van Herp, 1655, making it the oldest painting to be treated at the CNCR. All five of the paintings were bought in Europe in the 19th century by Eusebio Lillo (who also happens to have been the author of the Chilean national anthem) who donated his large collection of art to the museum upon his death in 1911.
Of the five paintings treated by the center, three were 21 x 29 inches, and two were much smaller, measuring 9 x 7 inches. Two had been previously cradled, and the rest were otherwise unrestrained. Four of the paintings were on copper, and one was painted on tin-plated iron. Various condition issues, all common with paintings on metal, were present; the most serious issues were corrosion (which consisted of brown stains and corrosion products protruding from the paint layer), distortion of the support, flaking paint, discolored varnish, and puncture holes where the paintings had been nailed to walls or altars. In addition, large areas of overpaint were present.
Treatment of the paintings began with documentation and an initial analysis of the imagery depicted. All of them appeared to be allegorical or religious, and a few were clearly similar in composition and subject to other, more famous paintings, such as the painting referred to as “Disciples of Emmaus” by the center, which featured two parrots that were exact matches to those in a Jan Breughel painting from c. 1620.
Cross sections of the paintings were taken in order to help conservators to distinguish between original and later paint. The four paintings on copper were found to have a lead white ground, and the painting on tin-plated iron had a ground consisting of Prussian blue and lead white. Varnishes were found to be mastic or dammar, but were clearly not original for several of the paintings. UV examination revealed aggressive cleaning and intervention in the past.
In order to determine the best methods for treatment, copper prototypes were created and used to test adhesion of various adhesives. The CNCR used Isabel Horovitz’s research into paintings on copper as the primary resource for their work. Following testing on the prototypes, corrosion was mechanically removed, and a solution of 15% B-72 in toluene was used to isolate the corroded areas and to consolidate flaking paint.
Distortions in the support were significant on a few of the paintings, and conservators hoped to be able to reduce it. Flattening was attempted on prototypes using a book press, and the result was considered to be less distracting. A few of the paintings were flattened in this manner. An acrylic plate was applied to the reverse to provide support and to allow the reverse of the metal plates to be seen.
15% B-72 in toluene was used as a base for filling losses in the paint surface, and a tacking iron was used to level the edges of the fills. Fills were isolated with a varnish and inpainted to a full visual reintegration. After cleaning and inpainting, the subjects of the paintings were revealed to be religious and not allegorical. The center has suggested re-naming the paintings accordingly, and has sent their proposed titles to the O’Higgins museum. The treatments and the revealed subjects will be summarized in an upcoming book.