Conservators Get to Know Guercino’s “Jacob Blessing the Sons of Joseph” cover

Conservators Get to Know Guercino’s “Jacob Blessing the Sons of Joseph”

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A few months ago, we began a two-year long conservation and research project of Jacob Blessing the Sons of Joseph, a Guercino painting in the collection of the National Gallery of Ireland. We are now gaining significant insight into the condition of the painting by using a variety of non-invasive analytical techniques.
This is the second post in the series, following the research and conservation of Guercino’s Jacob Blessing the Sons of Joseph by the Getty Museum and National Gallery of Ireland. To begin at the beginning, please click here.
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Conservators Get to Know Guercino’s “Jacob Blessing the Sons of Joseph”

July 26, 2016

A few months ago, we began a two-year long conservation and research project of Jacob Blessing the Sons of Joseph, a Guercino painting in the collection of the National Gallery of Ireland. As the summer temperatures begin to rise here in Southern California, the Guercino is keeping cool in the climate-controlled environment of our studio at the J. Paul Getty Museum, where we have been closely examining it.

We are now gaining significant insight into the condition of the painting by using a variety of non-invasive analytical techniques. Each technique, whether using visible light, ultraviolet (UV) and infrared (IR) radiation, or even X-ray, provides us with different and unique information that help us better understand the condition of the work as a whole, and, most importantly, how to treat the painting.

With Getty Conservation scientists Catherine Patterson (far left) and Alan Phenix (far right), Douglas MacLennan and Devi Ormond look at Jacob Blessing the Sons of Joseph under UV.

Our examination so far suggests to us that, overall, the condition is really quite good. There are some small tears in the canvas as well as areas of paint loss, and we have determined that the painting has been restored in the past, perhaps more than once. But, the painting’s condition is better than we expected when taking into account not only the painting’s age—over 400 years old, but also its large size—over 5 feet high and almost 7 feet wide (170 x 211.5 cm).

Examination Under Visible Light

Examination of a painting begins, of course, by looking at it under visible light (light that falls within the electromagnetic spectrum that is perceived by the human eye). In fact, most of the information about the painting’s condition can be gleaned from knowing how to look and what to look for—and that comes with lots of experience.

The way light hits a painting lets us see different things. We use several light examination techniques, including raking and specular light, to accentuate various aspects of the painting’s condition. The results are captured by our skilled photographers at the Getty and are included in our documentation files.

Two details of Jacob’s head from Jacob Blessing the Sons of Joseph, c. 1620, Guercino. On loan from the National Gallery of Ireland. At left, the detail is seen in normal light, and at right under raking light.

Raking light examination uses a single light source, placed at a low angle to the face of a painting. This placement of light emphasizes the surface texture throughout a painting. Raking light on the Guercino helps us see areas of previous restoration, as their surface texture does not match that of the surrounding original paint.

Detail of the head of Jacob as seen in normal light (left), and under specular light (right). In the image under specular light, we can see how much of Jacob’s facial features are obscured by the varnish layers.

Specular light examination places the light source directly behind the camera lens. This placement of light draws our attention to the gloss of a surface. When viewed in specular light, it is difficult to really see the details in the composition of Jacob Blessing the Sons of Joseph. This is because the surfaceis covered by a thick, shiny varnish.

Examination Using Ultraviolet Radiation

UV radiation is the region in the electromagnetic spectrum with wavelengths just beyond the blue end of the visible spectrum. Looking at a painting in UV can reveal things that we can’t see using our eyes under visible light. For example, many aged varnishes—depending on their composition—begin to fluoresce when they are excited by UV radiation.

In the case of the Guercino painting, the old layers of varnish, which have discolored over time, appear a dark yellowish brown in visible light. But, they fluoresce bright green when exposed to UV radiation! This green fluorescence suggests that the varnish may be an aged natural resin, such as dammar or mastic.

Jacob Blessing the Sons of Joseph as seen under UV. The dark patches suggest old retouchings.

UV examination can also sometimes reveal the locations of former restorations that may lie on top or even underneath a varnish layer. Against a brightly fluorescent varnish layer, the restored areas will often look dark. But, sometimes the fluorescence of a varnish layer is so strong that it veils old damage. This is one reason why using multiple examination techniques is so important to fully understand the condition of a painting.

Examination Using Infrared Radiation

Infrared radiation has longer wavelengths than visible light, and lies just beyond the red end of the visible spectrum. Many artists’ materials, such as varnish, and even some paint layers, become transparent under infrared. We can use this information to get a sense of the material make-up of underlying layers in paintings, especially if they are hidden by a varnish that fluoresces brightly.

Examining Jacob Blessing the Sons of Joseph using infrared has enabled us to visualize areas of old retouching that were obscured under UV.

Detail of the head of Jacob seen under UV light (left) and infrared radiation (right). Areas of damage appear lighter than the adjacent original paint, such as in the circled areas.

Examination Using X-ray

Sometimes we encounter cases where we find large and important sections of a painting that have been completely reconstructed by a previous conservator. To determine if the Guercino had undergone such treatment, we needed to assess the condition of the painting at every layer, including its canvas support.

The original canvas of Jacob Blessing the Sons of Joseph has been lined, meaning another canvas was affixed to the back of the original canvas in order to make it more stable. As a result, we can only see the back of the lining canvas. Any tears, holes, or other damages that may have occurred to the original canvas remain hidden.

The back of the painting showing the lining canvas attached to a wooden stretcher. The original canvas is no longer visible.

We can use high energy X-rays to penetrate the canvas and “see” the condition and appearance of the original canvas.

Fortunately, we have a lead-lined examination room in the conservation studio at the Getty, which enables us to safely X-ray a painting.

We learned from the X-ray that the original canvas support is in remarkably good condition for a painting this old and of this size. For the most part, the tears present in the canvas and losses in the paint layers are located around the edges of the painting. The figures and forms in the main composition appear to be intact, which came as a great relief—we now know it shows the original hand of the artist rather than that of a former conservator’s.

The X-ray image of Jacob Blessing the Sons of Joseph shows some small tears around the edges of the painting, and a couple larger tears, including at the middle right.

Detail of an X-ray image showing a tear in Jacob’s leg.

Detail of the X-ray image shows the twill weave structure of the original canvas.

The X-ray also revealed that Guercino used what is called a twill weave canvas, which has a pronounced diagonal pattern. This information adds to what is already known about the artist’s studio practice.

What’s Next?

Having collected a host of information from the initial technical examination of the painting, we can now write up a condition report and propose some treatment options that can be discussed with the conservator at the National Gallery of Ireland.

In the meantime, we have started to remove all the dirt and grime that can be found on the back and front of the painting. And, more imaging techniques and analytical tools have been carried out by conservators and scientists at the Getty. Hear more about other discoveries in our future posts.