Should Paintings Be Framed Under Glass?

By Mandy Moss

When you have a painting that you love, it is important to protect it so it can last as long as possible. While framing the painting behind glass may seem like the safest option, that is not always the case, and can actually cause damage if done incorrectly.

Should Paintings Be Framed Under Glass?

Should Oil Paintings Be Framed Under Glass?

The safest and shortest answer to this question is no. Oil paintings take a long time to complete the oxidation process, even after they feel dry to the touch. This “curing” process can take years after the painting has been completed, which is why you should wait at least six months before varnishing an oil painting, and at least a few years before putting it behind glass.

Doing either of these too soon may cause the painting to crack since the layers are still shifting during the curing
process. After the oil has completely cured, the pigments are protected by the oxidized oil, which is very strong and durable.

There is no need for framing oil paintings; the oxidized oil is strong enough to protect the painting against fading and dust. Placing a painting behind glass may cause moisture to become trapped between the glass and the oil paint, and this could result in the paint or canvas fibers decaying.

However, you may choose to protect an aged oil painting from outside pollutants, like dust or dirt, by framing it behind glass. Be sure to put a spacer in between the glass and the painting to allow air to circulate and prevent moisture from being trapped.

Should an Acrylic Paining Be Framed Under Glass?

Acrylic is different from oil because it dries much faster. It reaches a stable state within days under normal conditions, so cracking as it “cures” is not really an issue. The main problem with acrylic is how sensitive it is to heat. If it reaches about 86ºF (30ºC), the paint will soften enough that any dust or particles on the surface can be absorbed into the paint itself, and there is no way to remove the pollutants once they have incorporated into the paint.

This is the main reason people will choose to frame acrylic paintings behind glass. Similarly to oil, there is the risk of moisture becoming trapped between the glass and the painting and causing the paint and canvas to rot over time. Both acrylic and oil paintings need to “breathe” to avoid decay, meaning they need to absorb and release moisture on their own, with little interference.
If there is little risk of the acrylic painting getting up to 86ºF, then it is probably better to frame the painting without glass, but there is less risk in framing an acrylic painting than there is in framing an oil painting.

Should Paintings Be in Frames With or Without Glass?

There is no reason a painting needs to be behind glass, with one important exception: if the painting is on a material that isn’t canvas, then the challenge is preserving the material that holds the paint instead of the paint itself. For example, paper should always be framed, because paper is much more fragile than canvas.

Reasons to frame under glass

Let us discuss some of the benefits of adding glass to protect our art:

  • To protect warm acrylics from absorbing dust
  • To protect the surface from dust and soot
  • The painting is very old and extremely vulnerable
  • The painting is on or contains a fragile or sensitive material, like paper

Reasons to avoid framing with glass:

  • The painting is a young oil painting that hasn’t finished oxidizing
  • The reflective material of the glass prevents the viewer from seeing the painting clearly
  • To prevent mildew and decay from trapped moisture

If you decide to frame a painting without glass, do not hang it near a fireplace or candles, or harmful UV rays. (Direct UV rays should be avoided even if the painting is behind glass.) Beware of hanging it near lights that give off heat. Also, every few weeks or so, you can use a soft brush to gently brush away any dust that has accumulated.

What is the best way to frame a canvas painting?

The best way to frame a canvas painting is with a box frame. A box frame, also called a tray frame or shadowbox, is a simple frame with a neutral color- there is usually a small space between the edge of the frame and the canvas. It has the appearance that the canvas is resting in a tray that is made to fit it exactly.

These frames have a more contemporary appearance since their purpose is to emphasize the painting inside the frame, rather than add embellishment. It is rare to see a box frame with glass in front of the canvas.

Why are paintings in art museums sometimes protected by glass, and other times not?

There is no single answer as to why some paintings in museums are behind glass and others are not. It is preferable, for the best viewing experience, to frame a painting without glass. The reason is that glass is reflective, and while galleries are usually well-lit, there is no way to completely avoid reflections that will somewhat obscure the painting.

It is also difficult to see different textures in the paint when it is behind glass. A museum works with art conservationists on humidity and temperature in order to reduce the risk that acrylic paint softens when it becomes too warm. They also maintain older paintings by keeping them free of dust, and by reapplying varnish that has darkened with age.

Many paintings are centuries old, and usually, if they have survived hundreds of years without glass to protect them, it isn’t necessary to cover them now, especially in such a controlled environment.

Paintings that are behind glass, then, are usually special cases. The painting might be extremely fragile because of age, or might be exceptionally valuable. These cases are determined by art conservation experts, and the paintings are regularly checked to make sure that they aren’t being damaged by the display method.

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