Ask the Experts

Extreme studio temperatures

Karyn — Tue, 24 Feb 2009 18:22:00 GMT

Q: I currently keep all of my finished oil and pastel paintings in my Manhattan studio. In the winter, the studio gets very hot because I can't control the heat. Can the extreme temperature hurt my paintings?

A: Extreme changes in temperature are harmful to all works of art. A quick, or even a relatively slow change in temperature can cause stress on a painting, such as cracks in a paint layer or on the surface. I would recommend constructing an interior closet in the studio that is as far away as possible from the heat source. You can install a simple thermometer to monitor the temperature, and store artworks there when you are away from the studio. Another recommendation is to install ceiling fans to circulate the air and moderate the extreme heat.

Oil paint on paper

Karyn — Tue, 24 Feb 2009 18:21:00 GMT

Q: When I paint on paper with oil paints, it is all right to prime it with acrylic medium?

A: Just as it is imperative that you prime canvas to protect it from acids in the oil, the same is also true with any paper support. Gesso, acrylic polymer primer, would probably work the best. Acrylic gesso can contain calcium carbonate (whiting) and titanium white. Therefore, it will not only protect the paper from acrylic medium but will also provide a satisfactory ground for subsequent paint layer to adhere to.

Reusing thinner

Karyn — Tue, 24 Feb 2009 18:21:00 GMT

Q: Is it possible to reuse thinner or turpentine?

A: When you submerge your brush in a washer containing thinner or turpentine and wipe or scrub the bristles on the coiled wire or screen, the pigment particles will eventually sink to the bottom of the container, leaving cleaner thinner at the top. Similarly, if you empty the contents of a brush washer into a storage container, the pigment particles will settle to the bottom of it as well. After a few days of settling, you'll find that the thinner or turpentine is practically clear and ready for reuse.

Stapling canvas

Karyn — Tue, 24 Feb 2009 18:19:00 GMT

Q: I've heard that placing staples at an angle rather than parallel to the weave gives greater strength to a stretched canvas. Is this true?

A: Placing staples at a forty-five-degree angle to the weave of the canvas rather than parallel to it will tend to prevent the weave from separating at the point where the staple penetrates the canvas. When positioned at this angle, the two prongs come into contact with a greater number of threads than they would if the staple were placed in a parallel manner.

Staggering the placement of each individual staple in varying distances from the edge of the stretcher bars will decrease the likelihood of any separation of the weave during stretching. Using a close, tightly woven fabric also prevents separation of the weave.

Painting on raw linen

Karyn — Tue, 24 Feb 2009 18:18:00 GMT

Q: I like the color of raw linen and the effect I get when painting directly on it with oil colors, but I have been told that this practice is problematic. Do I have to use primer and give up my favorite way to paint?

A: It is not advisable to paint with oils directly on raw canvas-either cotton or linen-because this can make the fabric brittle as a result of the acidic nature of the linseed oil. You can, however, get almost exactly the same effect by painting on sized canvas.

Drying time for watercolors

Karyn — Tue, 24 Feb 2009 18:16:00 GMT

Q: I recently painted a watercolor that contained a larger, dark-brownish area where I combined Van brown, burnt umber, and green earth. In that spot, the paint took nearly two weeks to dry. What do you think occurred?

A: In general, the ingredients in watercolor (particularly the amount of glycerin in the paint) rather than pigments themselves that most affect drying time. Specifically, the colors you mentioned can be problematic. Green earth tends to behave like a clay in that it absorbs a good deal of water, particularly when applied heavily. And Van brown is not considered a permanent pigment: it tends to be unstable, whether used alone or in mixtures.

Another possibility that comes to mind is the opacity of your paint. If you applied the paint too thickly, the binding action of the paper on the pigment particles would lessen, causing the paint to dry more slowly and inviting the possibility of cracking.

Using a grisaille

Karyn — Tue, 24 Feb 2009 18:15:00 GMT

Q: What is a grisaille technique, and how can it help me?

A: Grisaille, as its French name suggests, is a monochromatic painting accomplished with shades of gray. Originally used by Greeks as a method of modeling forms and illustrating sculpture relief, it was also a standard method of painting indirectly (painting in layers) from the time of Cennino Cennini to the time of Ingres.

One of the most common uses for a grisaille, seen in numerous Northern Renaissance paintings, is an underpainting for flesh. The grisaille was often either a neutral gray or green color, although pink was also used for this purpose. The indirectness of the grisaille method will allow you to describe volumes in terms of light and dark values without the consideration of color.

Framing acrylic paintings on paper

Karyn — Tue, 24 Feb 2009 18:14:00 GMT

Q: I work primarily in watermedia and occasionally complete paintings done entirely with acrylic washes on paper or illustration board. How should I frame these works, and how does this method compare to handling oil paintings over paper?

A: Acrylic works on paper can be treated in the same manner as transparent watercolors or oils on paper. Although it's possible to show them unprotected, it's recommended that they be displayed under glass.

Stretcher keys

Karyn — Tue, 24 Feb 2009 18:12:00 GMT

Q: What are those strips of plastic on the back of my prestretched canvases?

A: Those triangles, attached to "trees" and stapled to the back of commercial canvases, are plastic version of wooden stretcher keys, which used to be provided with prestretched canvases. The keys can be used to tighten the canvas by expanding the stretcher bars if the canvas sags.

Too thin paints

Karyn — Tue, 24 Feb 2009 18:11:00 GMT

Q: I know what type of medium to add if the paint coming out of the tube is too thick. But what if the paint is too thin?

A: One way to alleviate this problem to some extent is by squeezing the paint out onto an absorbent surface such as blotter paper. With a painting knife, move the pile from one to another one the blotter paper in order to absorb as much oil as possible until the paint has the desired consistency. In doing so, you might find that after removing some of the oil, the true amount paint of in the tube is less than you had originally thought. Therefore, investing in higher quality colors may prove to be more economical in the long run.

Casein underpainting

Karyn — Tue, 24 Feb 2009 18:10:00 GMT

Q: I want to use oil glazes over a fast-drying underpainting, and I was told that casein is a good medium to use. Is it wise to paint on canvas this way?

A: Casein may be used as an underpainting for oil glazes. However, it's far too brittle to be painted on a flexible support, so you shouldn't use this technique on a stretched canvas. Once the casein underpainting has thoroughly dried, it will be far too absorbent to properly receive oil glazes: Your brush will snag and grab the painting surface, making smooth delivery of the oil glazes nearly impossible. Therefore, brushing or spraying a very thin size to seal the underpainting is required. Bleached white shellac that has been reduced with five parts of denatured alcohol works well for this purpose.

Purity of water in watercolor

Karyn — Tue, 24 Feb 2009 18:09:00 GMT

Q: How does the purity of water I use in my watercolors affect the color of the paints?

A: The luminosity and clarity of your watercolors are ultimately affected by the type of water you use. If these factors are important to you, then I do recommend using distilled water. However, it's fine to occasionally use water from an outdoor source when painting landscapes on location.

Old tubes

Karyn — Tue, 24 Feb 2009 18:08:00 GMT

Q: A friend gave me some old tubes of paint and I can't seem to open them. She suggested I hold a lighted match near the top of the tube and let the heat loosen the top. Is this safe, and will it work?

A: Opening difficult paint tubes using the method your friend suggests does work. On the other hand, a safer method is to place the tubes upside down in water that's heated to a boil. Submerge the tubes cap side down only to the neck, and in a very short time the caps will open quite easily.

Eliminating surface peaks

Karyn — Tue, 24 Feb 2009 18:07:00 GMT

Q: I sometimes get raised areas-points made of paint-on my paintings where I don't want them. Can I scrape these areas down with a pocket knife and the polish them with a burnisher?

A: These points or peaks are most likely the result of the way you apply thicker paint to the canvas and remove the brush. The best remedy is to avoid creating them altogether if possible, which can be accomplished by not removing the brush from the canvas at a ninety-degree angle. Instead, lift the brush off the canvas in the direction of the stroke. If at times you are unable to do this and a peak appears, eliminate the peak by flattening it with an unloaded brush while the paint is still wet.

Plexiglass for framing

Karyn — Tue, 24 Feb 2009 18:06:00 GMT

Q: What are the advantages of using Plexiglas for framing drawings and watercolors? I've been told that Plexiglas can harm paintings and drawings because it can chemically react with their surface.

A: Although it's highly unlikely that any kind of chemical reaction would take place between the artwork and the acrylic glazing known as Plexiglas, problems can arise if you allow the drawing or painting to come in contact with it. As a result, you should never allow the work of art to be framed in such a way that the glazing (even if it's glass) comes into contact with the work. I strongly advise that you use a window mat and spacer to provide at least a 1/4" air space when framing with Plexiglas.