42nd Annual Meeting – Paintings Session, May 29, 2014, "Oil Paintings on Metal Support: Study, Intervention, and Challenges" by Mónica Pérez

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.