Question regarding a Final Oiling Out and Temperature Effects on oilApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2019-04-16 11:07:04 ...
Most recent comment 2019-04-16 14:23:04
An observation was made on two types of finished oil
paintings: stretched canvas and canvas panel on paper hardboard, that reveal
some type of impact heat may have on the thin layer of walnut oil rubbed over
the final painting before varnishing.
After the first week of drying time, a nice oily shine
appeared on the canvas. At the end of the third week under much higher
temperatures (85 to 100 degrees F ), the surface now showed a visible dry and
flat appearance as if no walnut oil was applied.
Each painting used a quality canvas, received four (4)
additional coats of gesso and quality oil paints were used.
Did heat change the appearance of the walnut oil and it
remains on the surface, but not in a shinny wet appearance?
Did the heat evaporate the walnut oil product?
Did the higher temperatures allow for the oil to be absorbed
into the painting, requiring additional coats of walnut oil prior to the
application of varnish?
Your thought would be most appreciated!
Answers and Comments
First, I do not recommend the application of unpigmented
drying oils over painting unless these sections are to be covered with
additional pigmented oil paint. Look through our resources and do a search on
oiling out to read about our reasoning regarding this practice.
As to your questions regarding heat. It is true that
chemists understand that each rise in 10 degrees Fahrenheit, you get double the
reaction rate. In the short term, the temperatures you are describing should
have little effect other than to speed up the process that would occur
naturally over a longer period of time. In the long term the elevated
temperatures may contribute to premature aging, embrittlement, and desiccation
of an oil layer, oil paint film.
As far as evaporation, technically, oil films initially gain
molecular weight as they absorb oxygen. As they age, they do lose some weight
and components overtime. I doubt that this is what you are observing. My guess
is that the oil is simply drying more thoroughly and quicker than if the works
were stored at lower temperatures.
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