Beginning Level Activity
1. Display an image of the sculptures Mercury and Argus and Perseus and Medusa. Use the following questions to begin a discussion about the medium these sculptures are composed of. Chart student responses:
• What do you see?
• What is the dominant color in the two objects?
• If you could hold these sculptures, what would they feel like? What details in the artwork tell you this?
• How would you describe the texture you see on the surface of the sculptures?
• Based on your observations, what do you think these sculptures are made of?
Review the chart to summarize what students observed about the artwork and what they think it is made of. Students will record observations and predictions in their journals.
2. Pass around various porcelain objects so that students can feel some of the qualities of porcelain.
3. Explain that the sculptures are made of china clay, a mixture of water and very small particles of kaolinite clay. Divide the students into groups of three. Pass out small samples of clay, paper towels, magnifying glasses, and the Clay Observations student handout. Students will use these materials to look closely at the clay and describe what they see in writing. After students have finished their worksheets, have them share their findings. They should be able to identify the characteristics of clay, and describe how clay is different from the two substances that it is composed of (water and kaolinite clay).
4. Compare the observed clay characteristics to the students' observations from Step 1 about the porcelain sculptures. Students should note differences, such as the difference between the hard sculptures, and the soft and squishy clay. Explain that when china clay is heated by the sun, the water in the mixture evaporates and the clay dries out and becomes hard. If the dry clay is then exposed to higher temperatures in a large oven, known as a kiln, it goes through a chemical change to become porcelain. In a kiln, the minerals in the clay melt together to become very strong, hard, glasslike, and white.
5. Have the class sculpt a bowl or another simple shape out of their clay. Dry the sculptures in areas with different amounts of sunlight and heat: place some in a sunny window, some away from a window, and some in a dark area like a closet. Have the students check their sculptures every other day for a week to see how the clay changes as the water evaporates from the heat of the sun. Students should record their findings using the Clay Observations student handout. You may want to have students take photographs to record the changes in color.
6. After handouts are completed, discuss the class's findings and make conclusions about the how the mixture of water in the clay affects its properties. Students should be able to connect the changes in color, texture, and weight in the clay to the evaporation of water.
Intermediate Level Activity
7. While the students' sculptures are drying, discuss the two different processes that allow the water to evaporate from the clay, and then transform it into porcelain: radiation and convection.
8. The first process is called "radiation" and occurs when the water in the mixture becomes hot from the energy of the sun. As the water on the surface is exposed to heat, the atoms and molecules begin to move quickly. This motion creates energy, which changes the water molecules on the surface from a liquid into a gas. The gas then evaporates into the atmosphere. The drying of clay takes place slowly through this process as water molecules have to move to the surface of the clay and then evaporate into the atmosphere.
At this point, it would be possible to turn the dry clay back into a mixture of wet clay by soaking it in water. After their sculptures are dry, ask students to compare this dry clay to the sculptures of Mercury and Argus and Perseus and Medusa and ask "Do you think these sculptures would turn back into clay if you soaked them in water?" Explain that the heat from the sun is not strong enough to create the permanent chemical change in the clay minerals required to make their clay sculptures hard and waterproof porcelain, like the porcelain of the Mercury and Argus sculptures. Brainstorm with the class to come up with ideas to keep the clay from becoming soft again, to make it strong enough to not break as easily, and to make it waterproof. Chart responses.
9. The second process, which starts the process of transforming the clay into porcelain, is called "convection" and occurs when the clay is baked in a kiln. As the clay becomes heated from all sides, the heat transfers energy into the particles in the clay in the same way that the sunlight created energy in the water molecules on the surface during radiation. At first, the center of the clay remains cool, or still, because the energy has not yet moved to the center. Gradually, through convection, the surface heat travels into the clay, layer by layer, until the core heats up to the same temperature as the surface.
This heating must be done very slowly, however, or the clay may burn or crack. This is because, as the heat moves inward towards the core of the clay, the cooler molecules it encounters slow it down. If the heat is applied slowly, the temperature at the center will gradually become the same as the surface temperature. If heated too quickly, the surface molecules move faster than the interior molecules and burn the surface.
In order to be transformed into porcelain, the clay must be heated to very high temperatures, which causes a chemical change in the minerals of the clay to form the strong material known as porcelain. Artists bake dry clay in a kiln, at 2192°F–2552°F. That's 7 times hotter than your oven gets when you bake cookies! To maintain an unblemished surface and keep the clay from cracking, the heat must be raised slowly over many hours in increments of 300°F–400°F. It can take a few days to complete the process. This process is called bisque firing. Once the clay is turned into bisque-ware, it cannot be turned back into a wet clay mixture by adding water.
10. Partner with the art teacher at your school and have the students fire their dry sculptures in the school kiln. Students should note the time it takes to fire the clay and how often the temperature is raised. If you don't have access to a kiln, get examples from an art store of baked porcelain objects that have not been glaze-fired. Compare the surface of the baked clay to that of the sun-dried clay. Chart student responses.
Advanced Level Activity
11. Look at the reproduction of Mercury and Argus and Perseus and Medusa again. Ask the students the following questions: What other colors do you see besides white? How does the surface quality of these sculptures compare to the surface of the bisque-fired porcelain?
12. Explain that the porcelain was coated with a substance called glaze. Glazes are applied to ceramics to give the surface shine and protection and to add color. Glazes are mixtures of minerals, sometimes pigments, and silica. When these minerals are heated to high temperatures (often between 1972°F and 2269°F), they melt together with the silica to form a glasslike material. This process is called vitrification.
13. Explain the concepts of evaporation/melting, and condensation/freezing to students. Explain that energy is absorbed when a material evaporates or melts, whereas when a material condenses or freezes, energy is released. When heated in the kiln, the energy from the heat is absorbed into the minerals and silica composing the glaze, causing the molecules to speed up and melt together, which spreads the pigment out on the porcelain. When it cools, the glaze loses energy and solidifies to become hard and adhered to the surface of the porcelain.
14. Partner with the art teacher at your school to have the students apply glazes to their bisque-ware and to fire their sculptures in the school kiln. Students should note the time it takes to glaze-fire the sculptures and how often the temperature is raised. If you don't have access to a kiln, provide examples of glazed porcelain objects. Compare the surface of the glazed, fired clay to that of the bisque-fired clay.
|
 |
 |
|
| Mercury and Argus and Perseus and Medusa, Ginori Porcelain Factory, 1749 |
|
|
|
