Shedding light on a Picasso Teach article

Explore how researchers investigate artworks without damaging them and reveal hidden information in paintings by using different wavelengths of light!

In 2014, scientists and art conservators from the Phillips Collection, the National Gallery of Art, Cornell University, and the Winterthur Museum discovered the form of a man under the main painting of a Picasso artwork by using infrared (IR) technology. More specifically, a bearded man wearing a bow tie and supporting his head with his hand appeared beneath the famous Picasso painting The Blue Room.^[1] However, this is not the first time that a hidden image has been revealed beneath a painter’s artwork.^[2]

Technology and modern imaging techniques are constantly revealing new elements and hidden details of artworks, and thus, the way we perceive art is constantly changing. The main idea behind the use of the technique multispectral imaging (MSI) is as follows: the degree that radiation penetrates into the artwork depends on the wavelength of radiation. So, you can study different layers of an artwork by simply using different wavelengths of light.

Three main concepts underpin this technique.

The first is that light penetrates into the materials of the artwork to different degrees, depending on its wavelength (figure 1). The top layer (light blue) corresponds to the varnish, the next layer (green) corresponds to the colours of the artwork, the third layer (grey) corresponds to the draft, and the final layers are the canvas (white) and the wooden support (brown). Light (arrows) of different wavelengths reaches different depths into these layers: ultraviolet (UV) rays only up to the varnish, visible-light rays down to the main pigment, and IR rays down to the draft.

The second is the function of filters (figure 2). Filters only let certain colours or wavelengths of light pass through while blocking others. For example, a blue filter (left part) allows blue light to pass through but absorbs or reflects other colours like red and green. As a result, we can see only the blue paint colours because they are reflected. The other paint colours absorb the light, so we see black spots in those areas.

The third is fluorescence (figure 3). Some varnishes contain special molecules that absorb invisible UV light and then almost instantly (a few nanoseconds) release part of that energy as visible light. This is called fluorescence, and it makes the varnish glow in the dark when it is exposed to UV light.

By exploring different imaging techniques, students understand the interaction of light with matter, get familiar with applications of basic principles of physics in practice, and finally realize the interdisciplinary nature of scientific knowledge. This STEAM project aims to combine students’ love for both art and science, and it is suitable for students aged 14–18.

Activity 1: Multispectral imaging using UV radiation

This activity is related to UV fluorescence imaging, and takes advantage of the fact that varnishes used on paintings often fluoresce under UV light. Therefore, with this particular technique, it is possible to examine and diagnose the state of conservation of the painted surface of an artwork.^[3]

Time required: 40 minutes.

Materials

• 1 piece of watercolour paper
• Watercolours (or any water-based paint)
• Acrylic varnish
• UV lamp/torch light
• Student worksheet

Procedure

1. Start with engagement task 1, as described in the worksheet, by asking students to make their own hypotheses about how scientists managed to ‘see’ under the main painting.
2. Continue with task 2 and ask students to categorize radiation into visible or invisible to the human eye.
3. Go to task 3 and discuss with students what type of radiation they would use to study the varnish of an artwork.
4. Ask students to paint a picture using the paper and watercolours.
5. Cover part of the picture with the varnish.
6. Let the varnish dry for several minutes.
7. Illuminate the drawing with the UV lamp/torch and observe the fluorescence.
8. Ask students to alter their paintings by drawing over a small area of the varnish. Encourage them to work out how they could check if an original painting had been altered. Check their solutions on their paintings.

Results and discussion

In figure 4, one cloud is covered with varnish, while the other is not. If the painting is illuminated with normal lighting, then we see it as it is shown on the left. If painting is illuminated with a UV lamp, then areas that are covered with varnish appear brighter.

This happens due to the property of certain pigments of fluorescing in the visible region of the spectrum after excitation with UV radiation with a wavelength between 300 nm and 400 nm.

Varnishes, used on the surface of artworks, whether older or more modern, show this fluorescent property, in contrast to any later interventions or surface damage, which appear as dark spots without any fluorescent property.

Activity 2: Multispectral imaging using visible radiation

Imaging using radiation in the visible region of the spectrum gives us information about the artist’s work itself, since visible radiation penetrates the varnish and reaches a level below it. The use of different filters can allow the selective passage of light. Images of the painting are captured by a typical camera and can be converted into black and white (greyscale) for easy identification of areas that absorb radiation (black areas) and areas that reflect radiation (white areas), as shown in figure 6.

This activity can be implemented in two ways, depending on the age level of the students. In the first case, the filters are held in front of the camera. In the second case, a rotating platform is constructed and controlled by an Arduino microcontroller.

Time required: 40 minutes.

Materials

• 1 piece of paper
• Markers/watercolours (any type)
• 1 set of optical filters (e.g., a blue, a green, a yellow, an orange, and a red one)
• A camera that can be connected directly to a PC or an internet protocol (IP) camera that can be connected to a smartphone or to a PC via an IP network
• Smartphone (or router and PC)
• Student worksheet

Procedure

1. Go to task 4 of the worksheet and experiment with students using visible radiation.
2. Connect a typical IP camera to the smartphone, following the camera manufacturer’s directions, to see what the camera captures. Alternatively, the camera can be connected to a laptop/PC through a router. The drawing is placed in front of the camera, while various filters are inserted between the camera and the painting; these filters allow the selective passage of light through the camera lens.
3. Activate greyscale on the smartphone^[4] to easily identify the areas that absorb radiation (black areas) and the areas that reflect radiation (white areas).
4. Ask students to draw a picture with various colours.
5. Place the picture in front of the camera.
6. Hold one filter in front of the camera and ask students why some areas of the painting have black areas and others white areas.
7. Place all the filters one by one and observe how the brightness of a certain area (e.g., the blue colour of the Smurf) changes.

Extension activities

A nice extension activity is to build a rotation platform and program it to cycle through the filters. Rotation could be achieved with a servo motor that is controlled by an Arduino microcontroller.^[5] Also, PC software could be used to send commands to the Arduino controller to rotate the platform for specific angles. The Arduino sketch and the software that we made (source code and executable) can be found in the supporting material, along with full instructions for the construction of the rotating platform.

Older students can also get the intensity normalization of the captured images, and they can also construct a graph of intensity of the pixels of a specific area of the drawing versus the wavelength. This way, we get the ‘fingerprints’ of our pigments! Full instructions are given in the supporting material.

Results and discussion

This activity enables students to observe that, as we change the filter, different areas of the image appear brighter. For example, if we have a blue filter (λ_mean = 531 nm), the blue areas of the project appear brighter, while the red areas appear darker. Conversely, for the red filter (λ_mean = 693 nm), the roof of the house appears bright, while the blue areas appear dark. This is very useful from a teaching point of view for students, as they can understand the reflection and absorption of radiation, but also the fact that colour is not an objective property of matter.

In the art world, the study of different colours through the use of different optical filters enables art conservators to study the pigments the painter has used and check the authenticity of a painting.

Activity 3: Multispectral imaging using infrared radiation

Imaging using IR radiation uses the near-IR region (750 nm to 2500 nm). The radiation penetrates the first layer, which is usually the varnish, but can be the entire colour layer, and thus, reaches the artist’s draft (figure 8).^[6] Graphite, mainly used in an artist’s draft, strongly absorbs IR radiation.

Time required: 40 minutes.

Materials

• 1 piece of paper
• 1 pencil
• Markers/watercolours
• A camera that can be connected directly to a PC or an IP camera that can be connected to a smartphone or to a PC via an IP network. This camera must have a night-mode option
• Smartphone (or router and PC)
• Student worksheet

Procedure

1. Ask students to draw a sketch with a pencil.
2. Ask students to cover the sketch with markers or other paint, such as watercolours or oil paint. Avoid using the colour black.
3. Place the painting in front of the camera and set the camera to night mode (either by turning off the lights or by covering the light sensor of the camera).
4. Go to task 5 of the worksheet and ask students to answer the initial question: how did they manage to see under Picasso’s main painting?
5. For more fun, you can divide students into groups and ask each group to make their own drawing. Then, have the students guess what is under the others’ paintings.

Results and discussion

This noninvasive technique is often used by art conservators to discover hidden details or hidden images beneath a painter’s artwork. And this is exactly the case with many of Picasso’s paintings. In earlier times, many artists, mainly for economic reasons, painted on already-painted canvases, with the result that today we discover many hidden paintings under the main artwork. So, this constant revealing of hidden details in artworks is very important, as it changes the way we perceive art.

Conclusion

The specific experimental process is an opportunity for secondary school students to connect theoretical concepts found in school textbooks, such as the electromagnetic spectrum, photons, wavelength, and reflection, with the observation of suitable optical phenomena, which often exceed the limits of our own senses. Research at an international level shows that phenomena related to light and its properties are very difficult for students of all age levels;^[7–9] this is also confirmed by our own daily experience in the classroom.

The aim of this project is, on one hand, to help students face their personal preconceptions about visible light and its properties, especially with respect to light transmission, and to remove any misconceptions regarding invisible radiation, such as the origin of UV and IR radiation or the dangers and usefulness of each radiation. On the other hand, this project could be an alternative teaching proposal for teachers themselves. In the activities, materials found in school laboratories and free software have been used, while the cost of any additional component is low.

Finally, the project cultivates the students’ STEM skills because, during the implementation and execution of the activities, the students are confronted with various challenges at a mathematical, technological, and engineering level. At the same time, however, this specific project also encompasses the students’ love for the arts and the creation of their own ‘works of art’, because an interdisciplinary approach is followed to achieve the final goal.

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Supporting materials

Student worksheet

Extension activity

Intensity normalization

Graph of intensity

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