Paintings Need Support Too: Paper, Metal, and Glass

Paper is an acceptable support for most mediums including oil paint as long as good preparation methods are used. Paper can be made of all kinds of fibers, but the two main materials are wood cellulose and cotton. Paper manufacturing isn’t regulated so there is no standard to judge them by, but the top manufacturers have reputations to keep and will tell you the features of their paper.

For wet mediums like paint, cotton paper is the better choice as most cotton papers are acid free and tend to be thicker than cellulose. Cotton paper also mimics canvas to a certain degree since they are made out of the same thing, and you can expect a similar longevity. The best way to paint with oils on paper would be to mount the paper to a wooden panel, such as hardboard, and then size the paper and cover it with a ground. Watercolor or acrylics can be used directly on the paper, but you will get better results if watercolor paper is used since they have a thin size applied to them already.

Paper that is not acid free shouldn’t be considered for any work that you want to last as non-acid free paper will yellow and become brittle over time. A paper that is acid free and also buffered buys extra insurance since the buffering means the paper is slightly alkaline and will counter any small amounts of acid that come in contact with it.

Obviously, some of the biggest problems with paper as a support is that it can wrinkle, crease, and tear. Storing the paper in flat files will help with this, but mounting paper is probably the best way to prevent the problems. Also, paper will expand and contract with moisture just like any natural material, so for oil paint is has all of the same negatives as a natural cloth support.


Metal has been used for hundreds of years for paintings, but because it is relatively expensive and heavy it doesn’t see a wide use. Paintings of the Old Masters on copper are some of the most well preserved in the world with little or no cracking. Copper and aluminum have similar expansion and contraction coefficients as oil paint and aluminum is nearly identical with acrylic paint.

Some modern supports use sheets of aluminum sandwiched to a plastic core and are very good, but their price is still more expensive than wood, or cloth supports.

Thin metal supports should be avoided as the metal can easily be bent cracking the paint or even putting a permanent crease in the support which would transfer to the painting.


Glass would seem like an ideal support as it is smooth, rigid, doesn’t rot or expand or contract with air born moisture, but it’s fragile nature keeps it from being widely used. Also, some paint won’t stick well to glass and over time the painting could come loose.

Other Supports

As time goes on new supports are coming onto the market with both good an bad characteristics. Unfortunately, there is no way for me to cover all of them so the best way to choose would be to research them yourself based on the particular needs of your chosen medium. A great place to do that is

Paintings Need Support Too: Wood and Wood Products

Fayum boy 2nd century encaustic on wood panel
Fayum boy 2nd century encaustic on wood panel

Solid Wood

Wood has been used for centuries as a support for paintings with some good and not so good results. Wood naturally expands and contracts with moisture changes in the air, usually across the grain. This can lead to major cracks developing even to the point where the painting is no longer in one piece, as you can see in the picture above.

If wood is used it should be a close grained wood, and preferable a hardwood like poplar, birch, walnut, etc. Oak tends to have open grain and requires many layers of ground to fill them in, even though it was the most popular wood used in the past. Also, it is preferred that the panel be cut across the grain from heartwood to minimize expansion or contraction.

Even with precautions, including climate controlled environments, solid wood panels will have problems down the road. Many paintings on wood from the past are being transferred to more stable supports where possible, but since we have better options now solid wood panels should be avoided if there is not some compelling reason for using them.


Plywood is a much more stable support than a solid wood panel and is a good choice for a support. Plywood is a series of thin wood veneers glued together with the grain of each successive layer going in the opposite direction. Since wood tends to expand in only one direction, across the grain, the different layers pull against each other preventing the plywood from expanding or contracting much.

But all plywoods are not equal and lower quality or construction grade plywood should be avoided since the glue holding the layers together may not last as long and the support may fall apart. A cabinet grade plywood should be used for the best longevity as they are expected to last for many years and the wood used in them is a higher quality. Marine plywood should be avoided as chemicals are often sprayed onto the wood veneers to make them water resistant, but the chemicals could react with the size, ground, and paint of the painting preventing proper adhesion or other unpredictable results.

As with solid wood panels a hardwood plywood with close grain should be used. The surface veneers should be significantly thicker than several sheets of paper, especially if the laminate glue does fail and your painting has to be transferred to another support.


Hardboard is made up of millions of tiny wood particles that are compressed and are held together by either the natural lignan in the wood or by a resin. Hardboard has two main varieties, untempered which is held together with lignan and tempered which is held together by resin. Because of its density and multiple directions of the fibers, hardboard is less likely to expand or contract with fluctuations in moisture.

Artist’s were cautioned against using tempered hardboard since it used to be made with large amounts of oil, but with modern manufacturing techniques if oil is used at all a light sanding before sizing and applying the ground will take care of it. Also tempered hardboard is stronger and lasts longer than untempered since the natural lignan that holds untempered hardboard together will break down over time, and is more hydrophilic.

The question of which to use is becoming a moot question as untempered hardboard is becoming rare, leaving tempered hardboard as all that is available.


MDF, or medium density fiberboard is a compressed mat of saw dust that is held together with glue or resin. Due to the manufacturing process MDF usually has a smooth and hard outer surface with a comparatively softer less dense inner core.This is a concern for some artists as the inner core can absorb moisture, but this can be mitigated to some extent by painting the ground on both faces and edges.

Since MDF is softer than hardboard it is not recommended as highly, but it is still an acceptable surface for a painting.

General Concerns for Wooden Supports

All wood based supports will benefit from perimeter cradling and cross bracing on the back to prevent the panel from warping over time. It is recommended that anything 1/8 inch thick and over 12 inches square be braced by the addition of good wood strips glued to the back, except for a solid wood panel which would need a special bracing system. Gluing thinner panels to thicker plywood would also serve as a good bracing system.

If a panel is small, applying the ground to the back of the panel is a good practice as the pull of the dry ground will be countered by the same pull on the back. If you don’t want to use an expensive ground on the back, left over commercial household paint can also be used. But if a panel is cradled and braced, applying ground or paint to the back of the panel is not necessary.

Tomorrow we’ll get to paper, and hopefully also cover some of the more unusual supports.

Paintings Need Support Too

What a painting is painted on matters. As an art buyer or an artist you should know what you are getting, especially if you expect the artwork to last longer than you do.

Most people who buy paintings expect them to last hundreds of years, just like the paintings in museums. If the painting falls apart prematurely collectors will be disappointed and possibly angry. If you are the artist and you can’t repair the problem, you might have to fork over a refund.

The support, or what a painting is painted on, can be, and has been, all sorts of things with greater or lesser success. Some painters, like Albert Pinkham Ryder, painted on cardboard with food and tobacco juice, and now his paintings are falling apart and there isn’t anything that can be done to stop it. Other painters have used glass, plastic, metal, wood, cloth, paper, and anything else that is available, but the downside is that the longevity of the artwork becomes questionable when materials other than those that have been tried and tested are used.

The main supports throughout history have been wood, cloth, and paper and I’m going to focus on those, but I’ll briefly cover some of the other material’s obvious and possible problems.

Cloth Supports

Canvas is probably the first thing most people think of when they think about a support. Canvas is a heavy cloth made out of cotton, and is usually stretched over a wooden frame to give it stability. It was first used by the Venetians in Europe because it could be made into any size, was light in weight compared to a wooden panel, and was plentiful in a city based on sailing. Canvas can last for a long time, especially if it is kept indoors, but since it is a natural material it could rot over time if exposed to moisture and ironically, oil paint. Most oils are slightly acidic which if in direct contact with canvas will cause it to break down eventually.

Linen is the other natural fiber most commonly used for painting and is derived from flax. Linen is a longer fiber than cotton, and and comes in a larger variety of weaves from super smooth to rough. Linen can be stretched tighter than cotton in the beginning, but over time both fibers will loose their elasticity and sag similarly. Linen will also rot if exposed to moisture or oil. Some artists believe that linen will last longer than cotton, but historically they both have similar longevity. Since there are no significant handling differences between canvas or linen, the main reason to use linen is because it looks different than canvas.

Hemp can also be used for paintings and it has similar qualities to both cotton and linen. But hemp is usually a looser weave than either cotton or linen and so paint can push through the weave, exposing the back of the cloth to oils or water causing it to rot faster.

Polyester cloth shows promise for longevity since it’s not susceptible to rot, but it can only be primed with a heat set acrylic ground that has only been around for twenty years.

In general, cloth mounted to a rigid support will preserve your painting longer than cloth stretched over wooden bars, since paint tends to get more brittle with age and a flexible support will cause the paint to crack more. The rigid support could be wood, or a wood product like hardboard or MDF, or for maximum safety an aluminum panel.

All cloth supports should be isolated from the paint layers with a size, with the exception of polyester. A size is basically a glue, but all glues are not equal. Traditional size is rabbit skin glue, which is just a fancy name for hide, or animal glue. The problem with rabbit skin glue is that it is hydrophilic which means it will suck moisture out of the air, and as we already covered, moisture will rot natural fibers. Another problem with traditional size is that when it dries it tends to crack, which could cause the paint layer to crack.

A modern ph neutral PVA size should be used instead.

After the size a ground should be applied. A ground is a semi-absorbent paint-like surface that is usually white to maximize light bounce up through the paint layers. Gesso is the traditional ground and it is made of marble dust and rabbit skin glue. Gesso is no longer recommended for a ground on cloth because it is even more prone to cracking than rabbit skin glue by itself.

Acrylic “gesso”, which isn’t actually gesso at all, is an acrylic polymer usually mixed with titanium white pigment, and some sort of porous dust like calcium carbonate to make it more absorbent. Acrylic ground is flexible and can be used for either oils or acrylic paint, but oil paint will only have a mechanical bond to it and not a chemical bond which is slightly stronger. It is still in testing to see if the chemical bond matters. This may be a concern since oil paint becomes brittle over time and the flexibility of an acrylic ground may cause the paint to crack or flake off.

An oil ground is similar to an acrylic ground, but it doesn’t have the problem of not bonding with oil paint. And as with all oils it will become more brittle over time. An oil ground doesn’t necessarily have an absorbent material or dust added to it.

An Alkyd ground is resin modified oil mixed with titanium white pigment. It has much more flexibility and strength than a regular oil ground, plus it has the benefit of chemically bonding to the paint layer.

Next time we”ll talk about wood and wood products as a support.