94 The Chemistry of Art-Mid

The Chemistry of Art FOCUS Question How do the properties of matter help people create different forms of art?

There's Chemistry in Art From flat cave paintings to huge modern sculptures, visual art comes in many different forms. How do artists make art? The answer is chemistry. Early artists used the physical properties of rocks and minerals to paint on cave walls. Modern artists often use chemical reactions to create art. A chemical reaction changes a substance into something different. Let's look at some of the ways artists use chemistry to create art.

Earliest Colors By grinding soft rocks into colored powder, early humans made pigments. The colors of the pigments depended on the minerals in the rocks and the elements in the minerals. Ochre (OH-kur) was the first natural material people used as a pigment. Iron gives ochre a red or yellow color. White came from calcium in gypsum. Black came from animal bones, wood, or plants that were charred in a fire. The number of colors grew as people found new minerals.

Paint Sticks Around Paint is another way artists create art. Early artists experimented with substances called binders. The atoms in a binder hold the atoms in the pigment together. They also help glue the pigment to a surface. Animal fat, oil, and eggs are types of binders. The type of surface also affects how well paint sticks. When paint touches a surface, atoms in the paint bind to atoms in the material. Wood is rough, so it has a lot of surface area. Paint binds well to it. Canvas is not quite as rough, but paints bind to it, too. Plastic is smooth, so paint does not easily stick to it.

Clay Clay is a special type of natural material made up of minerals with atoms that are stacked in layers Between the layers. of clay are water molecules Clay can be air-dried. Some water molecules. escape during drying The layers of mineral atoms move closer together, and the clay shrinks a little. This is a physical change. But if it gets wet, the clay will break apart. Firing the clay in a hot kiln creates a chemical reaction and prevents breaking. At 1,000 degrees Celsius (1,832ºF), nearly all the water molecules are removed from the clay. At 1,200ºC (2,192ºF) and higher, all the water is gone. What's left is a strong grid of tightly packed mineral atoms. If it gets wet, the clay will not break apart. Creating Clay Pottery Step 1: The clay pottery is shaped on a pottery wheel and allowed to air-dry. Step 2: The clay pottery is fired in a kiln at very high temperatures. Step 3: The clay pottery is done. Water will not damage it now.

Glass Have you ever walked through a garden of colorful glass creations? These beautiful objects of art started out as a type of sand called silica. The elements silicon (Si) and oxygen (O) join together in a grid to form silica sand. Turning sand into glass requires an extremely hot furnace. Silica sand melts at about 1,600°C (2,912°F). At this high temperature, the silicon and oxygen atoms move apart in a chemical reaction. The solid sand transforms into a thick gooey (or viscous) liquid. Inside, the atoms are no longer in an orderly grid, so the molten glass can flow. Once the silica sand is liquid, a glassblower can form it into any shape. Do You Know? Adding different elements to melted silica can change its color. Copper makes it green cobalt makes it blue, and sulfur makes it yellow.