Ground Breaking Temperatures

It’s cold out there – or at least out here, in upstate NY.  And with the arrival of colder days comes concerns about lower temperatures and how these might affect paintings being stored or shipped in unheated conditions. For oils, the danger of dropping temperatures is focused mainly on the increased brittleness of paint films and the grounds they rest on. In a recent study by conservation scientists¹ on the impact of cold temperatures on various grounds, issues were raised about all the usual suspects.  But while it was long known that acrylic gessoes grew stiffer and more brittle in low temperatures, the degree this affected traditional oil and more modern alkyd-based grounds might come as a surprise.  At 68F/20C a traditional lead ground could only flex 1.6% before cracking, but by 50F/10C that was cut in half to .8%. As you fall even further down. to 32F/0C, that percentage was halved yet again, to just .4%, while alkyd-based grounds fared just slightly better, hovering around 1% or less. Just how little give and take does that represent? A 25” x 30” painting would only need to be keyed out or stretched a scant 1/16” to suffer a 1% strain in the corners and a .5% strain in the center of the canvas. So, for this example at least, an increased risk for cracking would exist even at the relatively mild temperature of 50F/10C. And of course, in all these cases, the older the oil painting becomes, the less flexible it will be.

So, what is a painter to do? Obviously the best solution is to keep your work in as moderate an environment as possible, and to avoid stressing or stretching any painting that might be colder than the typical, warmer room temperatures you find in a gallery or museum. If you can, try not to ship paintings during colder months, but if that becomes necessary, look for ways to dampen and minimize any flexing the canvas might undergo. And certainly by painting on panel, or mounting a canvas to panel, one greatly lessens these concerns altogether. Lastly, this is a great excuse to relocate to warmer climates – assuming you have been looking for an excuse in the first place.

Feel free to leave a comment and make sure to subscribe to get our next entry. And for more tips or advice, or just to chat about any of your questions concerning our paints, give us a call (800-293-9399 / 607-847-8843) or drop us an email techsupport@WilliamsburgOils.com.

Sarah Sands

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¹Young, Christina, and Eric Hagan. 2008. Cold Temperatures Effects on Modern Paint used for Priming Flexible Supports. In Preparation for Painting: The Artist’s Choice and Its Consequences, ed. Joyce H. Townsend, Tiarna Doherty, Gunnar Heydenreich, and Jacqueline Ridge, 172-179. London: Archetype

See also “Using Oils with Acrylics“, Just Paint 24, Golden Artist Colors


 

One thought on “Ground Breaking Temperatures

  1. In the Rembrandthouse in Amsterdam there is a small grisaille like painting, oilpaint on panel by Pieter Lastman. Although painted in the first half of the 17th century the quality of the paintlayers is impressively brilliant, as if painted just a month ago; and the thicker layers of the highlights and omberlike sketchlines are about .25 up to .50 mm thick and still in perfect condition: no craquele is to be found on the entire picture.
    Recent scientific publications and articles, including Golden’s, about grounds and its chemistry give rise to the following thought, after seeing the excellent state some old paintings are in.

    Perhaps a critical role is in the “hide” glue priming of the wood. Cennini and De Mayerne mention to apply three layers of glue, before priming. This glue is hychroscopic and that might be a clou: perhaps the center of the glue layer (as seen in a crosssection) might function as a “bridge” or lubricant between the side where the glue connects with the wood and at the other side where it connects with the gesso primer layer. And Humidity and air-temperature are interrelated in normal circumstances.

    Both a woodpanel and the layers of gesso have different rates of swelling or contracting stress (also see “Just Paint” issue 24) as do paintlayers. The wood picks up humidity from the air, as well as the gesso and paintlayers will do. And by this they both shrink or stretch with different rates. This diffence in rates is can be disastrous for the mechanical build up of the layered system of the painting, causing craquele.

    However, the inner core of the glue layer might also pick up humidity and gets “softer” or more flexible (or gets stiffer by dryer air or at lowering temperatures) and by this it probably can reduce the difference in tensions created by the different expansion or shrinking rates on its both extremities; bridging the tensions in the wood and the tensions in the gesso-primer.

    As far as I have found up to now, no research has been done or published about this possible positive effect of an intermediate glue layer. But when I see more paintings on wood, also in eggtempera and oil, dating from the fifteenth century onwards, being in perfect state, this hypothesis might be fair?

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