The Science of Chalk

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Edgar Wood
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1 Alex Nelson 1/8/17 Science of Paintings The Science of Chalk Chalk is a unique medium that has been used in a variety of ways in the creation of art. Both natural and man-made chalk has been an important tool to artists for thousands of years. The use of this marvelous substance can be observed historically through early cave paintings, limestone blocks used to build the pyramids in Egypt and through the marble statues of the great Italian sculptors (Tegethoff VIII, 55). Its unique properties allow it to be used for both drawing and priming. Chalk has been utilized in art in many ways. Since pre-historic times, chalk has been used in drawing since it is easily applied to a variety of surfaces including stone, paper and canvas. Its appearance can be altered for shading effects or smoothing by smudging. In addition to its use for cave drawings, chalk has been used for more sophisticated art works. Da Vinci, Raphael, Rembrandt, Rubens and Van Dyck as well as Matisse, Picasso and Degas are some well-known artists who used chalk in their works. Black and white chalk can be used for drawing contours and is particularly useful in creating portraits. Chalk can also be used to make sketches or outlines of figures in paintings to guide the artist (Encyclopedia of Art). Egyptians used chalk as a primer to prepare surfaces for painting. This technique continues to be used today, where chalk grounds are combined with glue and applied to the canvas. A primer does several things for the artist; it provides a smooth canvas, it creates a very white or reflective surface and lastly, it absorbs the paint (Tegethoff 56). Bright white chalk gives a luminescence to the canvas which can be exposed when the artist wants to create the effect of a bright light, especially when it is mixed with zinc white. This provides a pleasing optical quality. Painters can also create this 1

2 reflective effect by removing the applied paint to reveal the whiteness underneath (Tegethoff 57). Optical grays were used by many of the Old Masters. Here, a semi-opaque gray chalky ground created pleasing skin tones when exposed. A mat effect can also be acquired when the chalk ground absorbs the oil in the paint. The refractive index of chalk is very low so that it looks nearly transparent on the canvas when it is associated with oil (Dorener 31). Street painting is a type of performance art where the artist uses sidewalk chalk to create artistic images. It is uniquely ancient and contemporary and is a temporary form of artistic expression using chalk which is naturally worn away over time from pedestrians and from the weather. Although only more recently seen in the United States, this technique is thought to have originated in Italy in the 16 th century. These artists were essentially traveling minstrels who went from town to town, painting religious art on the earth or on the pavement in public squares using chalk, charcoal, bricks or colored stones. In modern times, these street paintings use interesting techniques such as the creation of 3- dimensional images or illusions. Festivals provide an opportunity for street artists to display their work and entertainment for the public ( A Brief History of Street Painting ). Chalk is made of calcium carbonate (CaC03). Calcite is the most stable polymorph found in nature. Limestone, chalk and marble are all forms of calcium carbonate. They differ in the arrangement of their crystals and the cohesion or sticking of the crystals to one another (Tegthoff 12). Limestone is a dense form of calcium carbonate and is a sedimentary rock. Limestone is believed to have been created during the Cretaceous period, million to 65.5 million years ago. Initially, lime mud was formed from the spines of marine animals, such as bi-valves, echinoids, ammonites, bryozoans and sponges. This material transformed to limestone when exposed to heat and extreme pressure. In a similar way, chalk was formed from single cell algae, resulting in tiny individual plates of calcium carbonate or coccoliths. (Harley, Tegethoff 40). Chalk is a powdery, less massive form than limestone of calcium 2

3 carbonate. It varies in purity and can contain sand, clay, iron, aluminum and magnesium (Blount 127). When chalk is exposed to extreme pressure under the earth s surface, it becomes marble (Blount 127). The Anglo-Saxons referred to chalk as Hwiting-melu meaning whitening powder. The Anglo- Saxons cut chalk around Dover on England s southern coast. These deposits are only one of many in Northern and Western Europe, including Champagne, northern Germany, the German Isle of Rugen, Denmark and Sweden. It was also used early in history in India and Japan (Tegethoff 44). The Latin word for chalk is crete, and refers to the Greek Isle of Crete where chalk has been quarried for thousands of years. The main reason for the widespread use of chalk was the ease with which it could be quarried and processed. Artist originally used natural chalk chipped off of larger pieces and sharpened. White chalk predominated and colored chalks came from areas where it was mixed with other elements. (Harley) During the 19 th century, classroom teachers and students began to use chalk more regularly on slate surfaces. Thus the manufacturing of chalk was necessary to meet demand. White and colored chalk is made from calcium carbonate derived from limestone. It is pulverized, further ground with water in rotating steel drums to wash away impurities and dried. Colored classroom chalk is made by adding dry pigments and the mixture is then sifted. Water is added, the slurry is extruded into sticks and baked at 188 degrees Fahrenheit for four days. Unlike mined chalk, manufactured chalk is generally dustless, because it is baked longer to achieve hardness. It is also dipped in shellac to prevent the chalk from coating the writer s hands. All chalk has a tendency to create powder and chalk manufacturing is monitored to ensure that the chalk does not create too much powder, which can be inhaled and cause lung damage. In the classroom of today, chalk is becoming a thing of the past. The use of overhead projectors and computerized digital graphic displays, which can depict motion, have decreased the need for an endless supply of chalk. However, we can argue that computerized technology demands more 3

4 preparation time from the teacher and removes the experience of an actively unfolding teaching environment in the classroom ( chalk ). Pastel, which is used similarly for art drawing, is manufactured from gypsum. Like limestone and chalk, gypsum is a sedimentary stone formed in ancient ocean beds. It is composed of calcium sulfate (CaSO 4). Pastel is created by adding colored clays or oils to the calcium sulfate slurry, which is typically air dried to maintain some moisture. Gum binders can also be added to pastel to create a chalk-like stick, which is softer and facilitates the blending of different colors more easily (Nikam). Chalk has many uses in addition to its applications in art. It is used in agriculture to give the soil a higher ph, making it more alkaline. Similarly, it is used in antacid medicines to help neutralize stomach acidity. In toothpaste, it serves as a mild abrasive agent to remove dental plaque. Chalk is also used as a whitening agent in cosmetics (Harley). In addition, it is used in sports to draw lines on tennis courts, football fields and baseball diamonds. Athletes, such as gymnasts, weightlifters and baseball batters, use chalk to create friction on their hands (Harley). Limestone and chalk are also used in the manufacturing of glass, the refining of metal ores and the production of construction materials such as concrete, mortar, and plaster. Its use is based on the chemical reaction referred to as the quicklime cycle. Material is selected for quarrying based on its composition and the presence of other minerals such as silicon and magnesium. Calcium carbonate is heated in a kiln to temperatures of 600 degrees Centigrade, which results in the release of CO2 gas and the production of calcium oxide (CaO), referred to as quick lime. This material is caustic and can be harmful to humans. When dry, quick lime is stable and can be stored or transported. The calcium oxide is then hydrated by adding water, which results in the formation of calcium hydroxide, Ca(OH)2, and is referred to as slaked lime. As slaked lime is exposed to atmospheric CO2, it is carbonated and reverts back to calcium carbonate. This is the process whereby pulverized limestone or chalk can be converted to concrete and plaster. When lime is used industrially in the production of glass, it is heated with silica 4

5 sand (SiO2) and sodium carbonate (Na2CO3), which results in a solution that does not crystallize when cooled. Instead, it hardens into glass, a solid which is amorphous, clear, and colorless. Lime is also used in the production of iron and aluminum. These metal ores contain large amounts of silicates. When lime is mixed with the ore and heated, the lime combines with the silica and forms a liquid called slag, which is immiscible with the molten metal and can be drained away from the metal. When limestone and chalk are exposed to acidic conditions naturally, calcium carbonate can dissolve into water. This can result in the formation of stalactites in caves as the calcium carbonate becomes less soluble and precipitates from the water. Similarly, when concrete structures are exposed to acid rain, damage occurs due to the loss of calcium carbonate. Depending on the composition of the soil, sometimes our well water can contain calcium carbonate. The degree of water s hardness is determined by the amount of calcium carbonate it contains (Tegethoff 4). When calcium and other heavy minerals are present in water, it is more difficult to rinse soap from our bodies as we bathe compared to the sodium salts of soap and detergents, the form in which they are sold. In conclusion, we see that chalk occupies a unique place in history. From primitive cave drawings to modern day portraiture, chalk has been very important in the creation of art and in providing educational tools for thousands of years. Drawing, writing and creating art have helped to propel our evolution as humans by fostering communication and preserving history. The manufacturing of chalk through the extraction of basic limestone and gypsum from natural quarries, created by the ocean beds, has provided a very useful and interesting compound for the artist and the teacher. 5

6 Works Cited A Brief History of Street Painting. Scientific American (1902): 235. Web. 14 Jan < Blount, Bertram, and A. G. Bloxam. Chemistry for Engineers and Manufacturers. Vol. 2. London: Charles Griffin and Co, Print. "Chalk." How Chalk Is Made - Material, Making, Used, Processing, Procedure, Product, Industry. N.p., n.d. Web. 14 Jan < "Chalk Drawings." Chalk Drawings: Types, History. Encyclopedia of Art, n.d. Web. 07 Jan < Doerner, Max, and Eugen Neuhaus. The Materials of the Artist and Their Use in Painting, with Notes on the Techniques of the Old Masters. New York: Harcourt, Brace, Print. Harley, Lukus. The Science of Chalk. Awesome Inc., 01 Jan Web. 07 Jan < Nikam, Kamini D., and Munira A. Hirkani. "Effects of Chalk Dust on Peak Expiratory Flow Rate in School Teachers." Effects of Chalk Dust on Peak Expiratory Flow Rate in School Teachers. IJMHS, 12 Oct Web. 08 Jan < "On a Piece of Chalk (1868)." On a Piece of Chalk (1868). Macmillan's Magazine (1868), n.d. Web. 07 Jan < Tegethoff, F. Wolfgang. Calcium Carbonate From the Cretaceous Period into the 21st Century. N.p.: Birkhauser, Print. 6

LIME STONE KILN using a wattle and daub technique

LIME STONE KILN using a wattle and daub technique This method of limestone burning uses a Kiln constructed of Clay mixed with sand and straw and will stand about 4/5 ft tall, mounted on four small legs,