A painting, like a house, needs a good foundation. If you are a professional artist, or are interested in permanence and would like your paintings to last for future generations to enjoy, you need to consider that the surface that supports your painting is of paramount importance. The following Questions & Answers will help you decide what is best for your needs.
Q: What does “permanence” mean?
A: If a painting maintains its original appearance in a typical, controlled interior environment for 100 years without cracking, fading, sagging, and so on, it is considered permanent.
Q: Should I paint on a flexible or rigid support?
A: Oil paint becomes harder and more brittle with age and is therefore more prone to cracking if the surface it is painted on is flexible and moving under the paint. For this reason, a rigid support is a good idea for oil paintings. For sizes larger than about 20x30" rigid supports made of wood or wood fibers are quite heavy and more subject to warping. It is recommended that you glue a wooden frame (cradle) to the back of large panels to prevent warping. At a certain size wooden panels become heavy and cumbersome, and the extra weight means they are more easily damaged if dropped and banged. This is the main reason why painters switched to using canvas for larger oil paintings. It is a trade off, but there are ways to improve the properties of the canvas to make it more permanent for use with oil paintings. See below.
Acrylics have not been around for hundreds of years like oils but scientific analysis and accelerated aging tests show that it will likely remain flexible indefinitely, like most plastics. Acrylics can be painted on a rigid or flexible support as long as they adhere well to the surface.
Q: Why is the ground important?
A: The ground, called a “Primer” for oil paintings, provides the ideal surface and absorbency for the paint to adhere to. The white surface of the ground ensures that the colors retain maximum luminosity as well. This is particularly important for oil paints which become darker and more transparent with age.
Q: Do I need to size the canvas or panel before putting on the gesso/ground?
A: Yes. Except for painting with acrylics on acid free canvas or paper where it is not essential for permanence. Wood or wood products are acidic and so a size is required to protect the acid from leaking thru the gesso or paint layer and causing discoloring. A coat of sizing is designed to create an isolating barrier between the wood and the paint or ground and to regulate the absorbency of the wood. It is a good idea to put a coat on both sides. For any type of painting or collage on panel a thin coat of white shellac (diluted 3:1 with Methyl Hydrate) is a good size. You must be careful not to put it on too thick or the surface will become too smooth and the ground will not stick well. Golden GAC 100 medium is also a good sizing material for wood panels or canvas. The water in the medium will cause the wood grain to swell and so it will need to be sanded smooth once it has dried.
Oil Paints are also acidic and will cause the canvas to deteriorate if it comes in contact with it. Here again the size acts as a protective barrier. The best material for sizing canvas for oil painting is PVA glue, or the Golden GAC 100 medium.
Q: Is acrylic polymer gesso a good ground for oil paintings?
A: It is difficult to say if the oil used to make the paints and the acrylic resin in the gesso will form a permanent bond since they are so different in their chemical and physical properties. When used on a rigid support like hardboard the oil paint will probably stay put as the absorbency and ‘tooth’ of the acrylic gesso does provide a good base. On canvas that moves, it is riskier – the flexible acrylic gesso will move with the canvas as it expands and contracts due to fluctuations in temperature in atmospheric moisture, but the oil will not be able to follow as well as it becomes more hard and brittle with age.
Q: What is the difference between the traditional gesso and the new acrylic polymer gesso?
A: For hundreds of years artists painted on panels using a simple gesso made of hide glue and calcium carbonate. This gesso is very absorbent and can be applied in very thin layers and sanded between coats to achieve a very smooth painting surface, more so than with acrylic gesso. The traditional gesso is very absorbent and needs to be sized before applying paint or it will absorb too much of the binder from the paint. The acrylic gesso substitute is made of acrylic polymer emulsion with calcium carbonate and some titanium dioxide and zinc oxide to make it whiter and give it more covering power.
Q: How about using white house paint from the hardware store as a ground instead of gesso?
A: This is acceptable for any painting that you don’t want to last. Artist’s materials are made with artists’ purposes in mind and for permanence. Industrial or commercial materials are made for other purposes and will have unpredictable results.
Q: What is the difference between cotton and linen?
A: Unbleached cotton for artist’s canvas is a cream color and has little brown flecks in it. Linen is a darker brown, burlap colored fabric. Linen is a much more durable fabric for a couple of reasons, but it is also more difficult to work with, esp. if you are stretching your own canvases.
There is a good way to prepare cotton canvas with acrylic polymers so that it will be as good or better than painting on linen. I would even use this method for preparing linen canvases as well. The Golden Paints company has two products that are perfectly suited to address the problems associated with a flexible, absorbent fabric like cotton that make it quite permanent.
Golden GAC 400 is a fabric stiffener and should be applied to the back of the canvas. This coating will also make it less absorbent to atmospheric moisture and so more stable in that regard as well. Apply the Golden GAC 100 to the front as a primer/sealer to make the fabric non-absorbent so oil cannot seep thru onto the fabric. The gesso/ground or oil based primer can now be applied over this medium.
Q: Can I paint in acrylics on cotton and get permanent results?
A: Yes. Acrylic polymer mediums, paints, and gesso will even act as a ‘plastic’ protection for the cotton canvas. It is also a good practice is to coat the back of the cotton canvas with gloss medium to protect the fabric and make it less absorbent.
Q: What is the best product for a rigid support?
A: Untempered Hardboard. Masonite is a brand name commonly used to refer to this product. It is inexpensive, very durable and easy to work with. It comes in 1/8” and ¼” thicknesses, smooth on one side, or smooth both sides. Hardboard is wood fibers compressed under pressure with the natural glue of the wood (lignin) serving as a binder to hold it together. No resins, glues or waxes are used in this product so it is quite stable. When properly sized it is very permanent. The tempered hardboard has oil added to make it water-resistant so it not recommended for use as a support because the ground and paint layers will not adhere well to it. All other wood products like chipboard, plywood, birch panels, melamine, etc., are not recommended for permanent painting practices and the glues used to hold them together may cause discoloring and will eventually dry out and cause the support to break down.
To prepare the hardboard panel, sand the smooth surface and put a thin layer of White Shellac, or Golden’s GAC 100, on both sides. Then at least 2 layers of gesso on the front. Hardboard panels are easy to ship and frame as well.
Q: How about a summary of some good choices for permanent painting?
A: For oils, acrylics, tempera paints, collage and mixed media, hardboard panels are excellent. In sizes up to about 16x20 1/8" hardboard is good unless you are doing very thick acrylic paintings or collages. 1/4" hardboard will be stable without warping too much up to about 20x30.” For panels larger than 20x30 it is advisable to attach wooden strips to the back to help prevent warping.
For oils on cotton or linen canvas, use the method described above to prepare it, then apply acrylic gesso or an oil-based primer. For acrylics or mixed media on canvas, or almost any synthetic fabrics, size on both sides with acrylic gloss medium, and gesso on the front.