Some Canadian oil paintings are starting to degrade. Saskatoon's Canadian Light Source helped discover why.

SASKATOON -- Scientists at the Canadian Light Source (CLS) in Saskatoon have discovered why oil paintings from the mid-20th Century have begun to degrade.

In partnership with the Art Gallery of Ontario, the Canadian Conservation Institute and the CLS, scientists examined experimental oil paintings by Rita Letendre, a Canadian abstract artist.

A unique characteristic of Letendre’s work is the use of impasto strokes - a technique where paint is laid on a canvas in thick layers which when dried, give the painting texture. Letendre, 91, from Drummondville, Que., is associated with the Automatistes.

• How scientists in Saskatoon are fighting COVID-19

Kate Helwig, senior conservation scientist at the Canadian Conservation Institute, says she used mid-infrared chemical mapping at the CLS to map out the layers of paint and figure out what’s causing degradation.

“There were a couple of different issues depending on the painting but in one of the works from the 1960s the paint seems to have an excess of fatty acids and in some cases those fatty acids have migrated to the surface and crystallized making a white snowflake crystals on the surface,” Helwig said of Letendre’s Victoire, 1961.

“In other areas those fatty acids had reacted in under layers with zinc pigments and that caused the under layer to be crumbly and to crack.”

• U of S team seeks to understand how asphalt behaves as temperature changes

According to the CLS, evidence indicates that paintings from the 1950s and 60s are experiencing these problems due to the combination of experimental techniques and additives paint manufacturers began to use.

Meaghan Monaghan, paintings conservator from the Michael and Sonja Koerner Centre for Conservation at the AGO, removed the white crystallization from the surface of Victoire, but scientists said it is possible the crystallization can recur.

Helwig said her research into the paintings showed degradation can be slowed by tightly controlling temperature and humidity.

• Rare dinosaur skin sheds light on evolution of prehistoric monsters

“Because the types of degradation going on are sensitive to changes in the environment so that (crystallized) snowflake material can return in the future if there are temperature changes,” she said.

Helwig added Letendre’s method of painting and the impasto technique are contributing factors in the degradation.

“Some of it has to do with the thick impasto and the fact that some impasto has added extra medium to make them smooth and flowing so those areas are more problematic in terms of being soft and not very well dried,” she said.