The Hidden World of Canvas Lining

How do you restore a nearly 400-year-old painting?

In the case of three giant canvas paintings held in the collection of the Galleria Nazionale d’Arte Antica’s Palazzo Barberini in Rome, the answer was animal glue.

A team of conservators undertook the structural restoration of these artworks in 2022, with a grant from Getty’s Conserving Canvas initiative. As part of the restoration, they attached a new canvas support to the back of each painting in a process called “lining.” Canvas paintings can age and lose strength over time. Lining can reinforce their structure and help prevent future damage.

There’s no singular lining approach that works for all paintings. Different methods use varying degrees of heat and combinations of natural and synthetic materials ranging from flour and beeswax to lab-grade adhesives to attach the canvases to each other. The end goal, however, is always to safely provide support for worn paintings with minimal intervention.

“There’s Curiosity and Doubts”

To treat Palazzo Barberini’s paintings, the group adapted glue-paste lining, a method using a mixture of water, flour, and animal glue (more on that later). Matteo Rossi Doria, a paintings conservator who worked on the project, is one of the few specialists formally trained in the glue-paste method. He dedicates much of his time to teaching others how to line paintings. “There’s no one way to do things, and how methods overlap and draw from one another has a lot to do with human relations over time,” Rossi Doria says. “There’s curiosity and doubts among conservators, but I want to fill the knowledge gap and see what happens.”

These doubts can be traced back to a major international summit in the early 1970s, when specialists from around the world gathered to debate what defines a good lining. “Conservators were noticing that different lining techniques can negatively impact the material and physical characteristics of paintings, including causing color changes,” says Lori Wong, senior program officer for conservation grants at the Getty Foundation who heads the Conserving Canvas initiative devoted to upskilling professionals on lining and the latest advances in the field. “The 1974 Greenwich Comparative Lining Conference was the first time conservators talked together about the observed effects of lining and what to do about it.”

The event opened conservators’ eyes to the need to further research and adapt existing methods, some of which, like glue-paste lining, were carried out in the same way for centuries. There was even a call for a moratorium on lining to give conservators a chance to step back and develop less invasive techniques.

What that means today, in short, is that lining is complicated. Conservators need to consider a painting’s history, ranging from the materials used, environmental conditions, and whether it has already been lined, before deciding how to line it, if at all. Many conservators agree that a lining is deemed successful when it leaves no visible trace on the artwork’s appearance. Take a peek beneath the surface at the hidden methods they’re using to keep many of the paintings you see in museums in top shape.

Glue-Paste Lining

Now, about that animal glue. Glue-paste lining is a traditional method dating back to the 16th century. Conservators paint the back of a painting with a concoction of animal glue, flour, and water before adhering the second canvas with heat. To protect the paint layer, a “facing” consisting of tissue or another cellulosic material is first applied over its surface.

The technique relies on non-toxic, readily available materials, but the use of water and heat can raise concerns around moisture levels and the deterioration of these organic ingredients. “It’s a very complex issue,” says Rossi Doria. “There are a lot of nuances among these materials that conservators usually do not consider since we were taught they behave in a certain way.”

Rossi Doria has spent decades researching water-based adhesives and comparing different recipes to create a path forward for caring for the countless paintings that have been treated this way. He even worked with scientists in food engineering, cosmetics, and medical industries to delve deeper into why materials like flour and animal glue behave the way they do.

“That opened up a new world for me,” Rossi Doria says. He and the Palazzo Barberini team were able to determine that slight tweaks, like increasing the protein content of the flour or using less water in the mixture, yielded better results. So, too, did mixing in synthetic adhesives like an acrylic emulsion. While the latter is not a standard procedure, it proved to be a promising experimental approach. “We want to offer restorers the opportunity to reflect on the use of water-based adhesives that have been passed down through tradition after bringing them up to date,” he says. “The conservation community needs this method and needs to do it better.”

The Dutch Method: Wax–Resin Lining

Wax-resin lining, aptly nicknamed “the Dutch Method,” was developed in the Netherlands in the 19th century to address tears, holes, and flaking paint as well as some of the problematic effects of glue-paste linings of the time, like mold growth and insect infestations. While the two treatments share a similar application process, this one has a few key differences.

Wax-resin lining uses heat to saturate the painting with the lining adhesive composed of beeswax and natural resin. Compared with glue-paste lining, the process requires no water, which reduces the risk of canvas shrinkage. Furthermore, the wax-resin adhesive is not prone to mold growth.

The method was used intensively until the 1970s when specialists discovered that it could change the surface texture, color, and chemistry of paint. Emilie Froment, a paintings conservator at the University of Amsterdam who has hosted wax–resin workshops through Conserving Canvas, encourages professional conservators to explore the technique—especially because this knowledge is no longer widely available. She even got her PhD on the subject, researching how wax-resin lining may have affected the color in Rembrandt’s The Night Watch.

“Clarifying the factors that may cause color change after wax-resin lining aims to guide treatments such as cleaning and retouching,” she says. “I try to give conservators a guided path to understanding more nuanced approaches and spark more research into the effects and consequences of the method.”

Mist Lining

Mist lining offers a modern take on traditional lining methods, using acrylic resin sprayed onto the added canvas to create a flocked adhesive layer applied to a network of fibers that is then activated with solvent vapors and under light pressure. It’s a gentler, more flexible approach that doesn’t use temperature or moisture during the lining process. Nor does the lining adhesive saturate the original canvas or paint layers, making the lining canvas easy to remove.

Paintings conservator Kate Seymour says the method embodies a new mindset toward the goals of conservation, especially the structural repair of canvas paintings. “We’re moving away from providing additional support that is more rigid than the original surface,” she says. “We’re incorporating that natural feeling of the canvas, retaining the flexibility of the original support, and that may mean the linings don’t achieve the same results that other traditional lining methods do. But there is no change in appearance or color of the paint layers and the authenticity of the artwork is prioritized.”

Mist lining is a newcomer to the world of canvas painting conservation. It was developed by conservator–restorer Jos van Och in the 1990s at the Stichting Restauratie Atelier Limburg (SRAL) and has since been successfully used to line large-scale works and paintings previously lined with wax–resin or glue–paste adhesives. “I hope people will continue to develop and use this technique,” says Seymour, a colleague and mentee of van Och who has led Conserving Canvas mist–lining workshops around the world. “There’s so many nuances and variations that conservators need a little bit of confidence and experimentation to master the technique, and that means time and support, which our team is willing to provide.”