You don’t really expect a seemingly dry painting to suddenly start oozing streaks of wet paint, seven years after its completion.
So when Otto Piene’s Harvest
Taking a closer look at several of these paintings, Schulz figured out something that all the weeping paintings had in common: The tears occurred in places on the canvas where the artist has laid down a thick layer of oil paint.
Although the thickly-laid paint seems to dry, it turns out to be unstable and capable of liquefying. But why? It’s not as if applying thick layers of oil paint is a new thing among artists… Yet the weeping painting issue is relatively new, having emerged in the last two decades or so.
What’s changed, Schulz says, is formulation of oil paints. Until recently oil paint was made using linseed oil. But the problem with linseed, she says, is that it has a tendency to yellow over time.
So paint formulators began exchanging linseed oil for sunflower oil, because sunflower oil doesn’t yellow.
The problem is that sunflower oil doesn’t dry as well. That’s because the oil contains fewer reactive double bonds, which are required to form a permanently dried paint complex, Schulz says.
Thick layers of the sunflower oil paint may seem to dry, but they are unstable. Subjected to changes in temperature and humidity or even the jostling that occurs during transport, these layers can collapse, releasing component parts as a gooey tear running as fast as 2 centimeters per month.
Other paint components can help or hinder the instability, Schulz says. For example, formulators have been increasingly replacing lead-based pigments for titanium- or zinc-based ones in white paint. Unfortunately, lead seems to help paintings stay stable, while replacements are not as effective.
Additional ingredients in oil paints such as bees wax (used to stabilize pigments) and aluminum stearate (used to improve viscosity) may also play a role in the ability of sunflower-oil paint to dry completely, Schulz adds.
She’s currently developing recommendations for formulators and artists on ways to avoid the weeping painting problem—and she’s also working on strategies for conservators tasked with stopping the flow.
As an aside, paintings aren’t the only cultural artifact to shed tears:
Plastic artifacts are also notorious weepers.
Here’s a photo of one of the first crash test dummies used to check seat belt safety in the 1970s.
The mannequin is made out of PVC plastic whose orange phthalate plasticizer is quite literally oozing out, leaving sticky drops on the display case, until conservation scientist Yvonne Shashoua came to their rescue.
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