Why Do Conservators Attach Backing Boards to Paintings Post-Treatment?

As conservators, we focus primarily on safeguarding the integrity and longevity of paintings under our care. Part of this is attaching backing boards to each painting if possible. This is one of many preventive conservation techniques we employ. Specifically, backing boards provide structural support and protect from environmental threats. Let's explore the many reasons we attach backing boards.

The Role of Backing Boards in Conservation

Backing boards are rigid or semi-flexible panels attached to the back of a painting’s stretcher, strainer or frame. Typically cut from stable, conservation-grade materials, these boards physically reinforce the painting’s verso. Materials are meticulously chosen so they do not chemically interact with the painting.

The primary function of a backing board is to provide a protective barrier against mechanical damage, environmental fluctuations, and pests.

Historical Context of Using Backing Boards in Conservation

Historically, the use of backing boards in conservation and restoration was more archaic. It involved using materials that, by today's standards, would be considered harmful to the painting itself. The ways in which our approach to creating and attaching backing boards mirrors advancements in conservation science, which now informs most painting conservator’s practices.

Modern conservation practices have shifted toward archival-quality, acid-free materials that promise long-term protection without damaging the canvas. Our understanding of the complex interactions between art materials and their environment is always evolving, however. It’s important to reassess materials used for backing boards in contemporary conservation strategies as new options and scientific research emerge.

Reasons for Attaching Backing Boards

Prevention of Punctures and Scratches

Backing boards play a key role in protecting paintings from punctures and scratches, which are common risks for paintings, especially those on thin boards or canvas. The rigid structure of the backing board acts as a shield, absorbing impacts that could otherwise tear, stretch, or scratch the canvas.

We are particularly insistent about the use of backing boards for paintings that are frequently moved or those in high-traffic display areas, where the likelihood of accidental contact is far higher.

Shielding from Other Handling and Transportation Risks

During handling and transportation, paintings are susceptible to a variety of physical threats–not just those from the handlers themselves. Backing boards provide a stable support that prevents the stretcher or strainer from flexing.

This added rigidity helps maintain the painting's structural integrity, especially during transit, when vibrations and abrupt movements are common. Of course, additional safety measures are needed when transporting a delicate painting.

Mitigation of Humidity and Temperature Fluctuations

Backing boards also mitigate the impact of environmental fluctuations on a painting’s canvas (from the verso) and sometimes on its stretcher or strainer. Variations in humidity and temperature can place stress on paintings, leading to greater deterioration over time. If the appropriate material is chosen, the backing board acts as a barrier, buffering the canvas from rapid changes in the surrounding environment. This can extend the painting’s life, as it helps prevent the detrimental effects that result from the expansion and contraction of materials in response to unmitigated environmental changes.

Reduction of Canvas Expansion and Contraction

The physical response of a canvas to environmental conditions, notably expansion and contraction, can be detrimental to the integrity of the paint and the canvas itself. Backing boards can help prevent the canvas or secondary support from changing in response to humidity and temperature changes, but it cannot counteract a particularly unstable environment.

However, some backing boards do trap moisture and cause their own microclimates. As such, it is important to select the materials carefully and check the painting's verso intermittently.

Structural Support for Lax Canvas and Heavy Paint Layers

A six-part backing board in progress. Off-set clips, metal plates, and screws will be used to attach the boards to the stretcher and cross bars without puncturing the tacking edge that folds to the back.

Another important function of backing boards in painting conservation is supporting a sagging canvas, which can occur under the weight of thick, heavy paint layers. To support heavy paint layers or heavy canvases, conservators often incorporate batting or archival foam supports between the board and the canvas.

These materials provide gentle, yet firm support, distributing the weight of the paint and relieving stress on the primary support. This method effectively prevents the canvas from drooping forward or backward and distorting over time. It also protects paint from cracking or tenting as the result of a flopping canvas. Adding a supportive layer light batting helps in maintaining the painting's original tension and form when tapping out keys is not an option.

Insect Access and Damage Prevention

Insect damage is one of our greatest concerns in painting conservation. Various species, including wood-boring beetles, silverfish, and booklice, all pose threats to paintings. These insects can damage the canvas, the wooden stretcher bars, priming, labels, and even the paint layer itself.

Their feeding, web weaving, droppings, and nesting activities can lead to physical deterioration of the artwork, including acidic splatter, discoloration, holes, and loss of material. The risk is heightened in environments with high humidity or organic materials, which insects prefer.

Backing boards are an effective measure against insect damage and gathering dust. By creating a physical barrier, these boards prevent insects from accessing the canvas and stretcher.

A Place to Attach and Display Encapsulated Labels

In the course of conservation treatment, labels or other identifying markers that were originally attached to the stretcher or strainer of a painting may need to be removed and protected. These labels often have important information about the painting, i.e., ownership and provenance, exhibition history, and artist details. Once removed, these labels are always stabilized if necessary and encapsulated to preserve them from any further deterioration, from staining the canvas, or from attracting insects. The adhesive used to attach labels to paintings is often of interest to insects.

The backing board then serves as a logical spot to reattach these encapsulated labels. This method ensures that important historical and contextual information remains closely linked to the painting itself, while being protected from environmental factors that could contribute to its degradation. Maintaining the link between the painting and its historical documentation in a secure and non-intrusive manner is vital, and something we take very seriously as conservators.

We also take photos of any signatures or inscriptions on the verso of the canvas that might be obscured by the backing board. If possible, we will create a window in the backing board for inscriptions, covered by a thin sheet of mylar.

Materials and Techniques in Backing Board Application

Archival board is commonly used in backing boards due to its durability and lack of reactivity. These materials are specifically designed to be chemically stable, ensuring they do not emit harmful gases or adversely react with the painting in any way.

Process of Attaching Backing Boards to Paintings

We carefully cut and attach backing boards to paintings so that we avoid any possible damage. Conservators use as few screws as possible to avoid creating too many holes in the stretcher, frame, or strainer. Whenever possible, we use existing screw holes to limit the need for new punctures.

For larger paintings where handling can be challenging, we might design backing boards with hand-hold cut-outs. These cut-outs make it easier and safer to handle the painting, reducing the risk of damage during transportation or exhibition.

Considerations for Different Types of Paintings

As with any conservation campaign, different types of paintings require different approaches when designing and attaching backing boards. Factors like the painting's age, the materials used by the artist, the condition of the canvas or panel, and the size of the piece influence our choice of backing board material and attachment style.

For instance, older paintings or those with fragile surfaces may require a lighter, more supportive backing board. Larger, heavier artworks might need a sturdier board with additional support features like the batting mentioned above. Each painting's unique characteristics dictate the specific methods and materials to be used.

Final Thoughts on the Importance of Attaching Backing Boards to Paintings

Backing boards play an important role in shielding paintings from physical damage, environmental fluctuations, interruptions to structural stability, insect damage, and more. They also provide a platform upon which to preserve labels that track the painting’s history. Using archival-quality materials in backing boards ensures that these protective measures never compromise the painting’s integrity.