Future topics to be developed: delamination, craquelure, buckling, fading colours/lightfastness, patches/stains of semi-gloss after varnishing, brushes, cleaning, studio lighting, self-portrait setup
Yellowing Of Oil Paints
In my experience, most of the yellowing we see in old oil paintings is in the old varnish, and once that is removed, the yellowing of the paint itself is usually negligible, unless the painting has been recently stored in a dark place.
Linseed oil paints do yellow somewhat, but the yellowing is a temporary phase they go through that eventually reverses if the painting is exposed to light. That being said, the Old Holland Cremnitz White samples on my test panels yellow more than the others on the same panels, and remain yellower for a longer period of time. My guess is that this is due to their stabilizer, hydrogenated castor oil, which the manufacturer doesn’t want us to know is in there.
My personal feeling is that concerns for yellowing of oil paints are overblown, because the initial yellowing of linseed oil paints reverses with exposure to light, as I mentioned in my book. If the painting is kept in darkness, the yellowing will return, but will bleach out again if the painting is returned to the light. How fast these changes occur depends on the strength of the light the painting is exposed to.
Using stretcher or corner keys to tighten loose canvas on stretcher bars is not a best practice.
“The problem with using corner keys to tighten slack canvas is that it creates uneven tension, tighter in corners than anywhere else, because the staples or tacks along the sides are still the same distance apart from one another. This seems to work well enough in the short term, but can create problems after the canvas is no longer new. A better practice is to remove all the staples or tacks, and re-stretch the whole thing, using copper tacks instead of staples. Better still, glue the canvas to a rigid panel.”
White Spots on the Canvas
Symptom: White spots on a canvas that has been stored in a damp studio. Could it be bloom or mold? How should one deal with it?
The white patches could be bloom instead of mold. This is something conservators have started finding recently in oil paintings from the 1960s and newer. It’s suspected as being caused by aluminum stearate, a stabilizer that most brands add to their oil paints to prevent the oil and pigment from separating in the tube while the paint is waiting to be used.
If the spots are mold, try brushing them off with a clean, dry, stiff hog-bristle brush, while wearing a mask to prevent inhaling any mold or spores that become dislodged. The best advice, however, is to take it to an AIC-certified conservator.
Removing Creases from an Unstretched Oil Painting on Linen
Symptom: Is there a way to remove creases from an unstretched oil painting on linen? My husband laid something on top of one of my paintings and somehow it got folded over and now has a large diagonal crease.
I’d suggest stretching it tightly enough to straighten the crease out of it, using metal-head push pins as tacks, and leave it that way for at least a few days. Then remove the painting from the stretchers and glue it to a rigid panel with a bracing framework glued to the back, and tack the edges of the canvas to the braces, stretching it while the glue is still liquid. I’ve done this enough times by now to be able to do it without an assistant, but if you have someone who can help you, it will be easier and less time-consuming.
The adhesive I use is BEVA 371 film, which is reversible with heat in the 130-140-degree Fahrenheit range. It requires heat to liquify it. When I do this, I first adhere the BEVA film to the panel, then carefully position the canvas on it and cover the canvas with a fairly thick cotton sheet. I use a regular laundry iron adjusted to the cotton or wool setting, and start ironing in the center of the canvas, keeping the iron moving constantly, going first from the center to the middle of one of the long sides, stretching and ironing at the same time, and then putting a push pin in. Then move to the opposite side and do the same thing, keeping the iron in motion constantly while it’s on top of the sheet to prevent it from scorching the painting. The procedure is the same as stretching on stretchers, but with the added task of ironing at the same time; essentially a juggling act.
The benefit of using this adhesive is that you can remove the canvas and redo it if it doesn’t turn out well on the first attempt, and in your case, the iron will help flatten the crease. There is a potential downside as well, in that the painting could be scorched if the iron is not kept moving or if it’s hotter than it needs to be to liquefy the adhesive. I scorched one of my paintings the first time I did it, but I fixed it by scraping out the scorched part and repainting it. Anticipating that possibility, shoot good photographs of the painting before you begin, so you can use the photos as a guide in case you need to fix it after scraping out a scorched part.
You might try doing this with a blank canvas first, in order to gain experience that will help you do it successfully when you’re doing it with one of your paintings. I would only do this with my own paintings because I can fix them if I mess up. With other people’s work, we shouldn’t risk screwing it up. Professional conservators are who should be entrusted with this task.
For the future, I suggest not painting on loose canvas. Stretch it or mount it before you start putting paint on it.