Category Science

HOW ARE CLAY ARTICLES SHAPED?

Clay can be shaped when it is wet by squeezing it between the fingers, “throwing” it on a potter’s wheel, or pushing it into a mould. Before using any of these methods, the potter must make sure that there are no air bubbles in the clay. If there are, the air will expand when the clay is baked, and the article may explode, breaking other items in the kiln as well. However ceramic articles are produced, they are made a little larger than the finished product needs to be, as they shrink slightly when baked.

1. Start off with clay of the proper consistency: soft enough to throw easily, yet not so soft that it will quickly collapse. Clay that’s too hard or dry is very difficult to throw. Be sure to wedge the clay carefully up to 100 times, taking care not to fold it in a way that might trap air bubbles within. Mold into as perfect a cone shape as possible, and smooth out all cracks.

2. Slam cone onto the center of the wheel head or bat. Slowly spin the wheel to see if clay is off center; if so, gently slide cone toward the center as much as possible while the wheel is turned off.

3. Thoroughly wet the clay and start wheel turning to begin centering process. Cup hands evenly around clay and force cone upward and downward a few times to align the clay particles. Then firmly press inward with one hand, and downward with the other, making sure the entire exterior surface of the clay hump is in contact with a portion of the hands. Keep hands firmly positioned in one spot, and with wheel spinning rapidly, steadily maintain that position until the clay offers no resistance, periodically wetting it as necessary. Whenever you remove your hands from the clay, be sure to do so SLOWLY, so as not to knock the piece off center.

4. Once the clay is centered, cup hands around it and allow thumbs to glide into center while wheel is turning. Press slightly to make dimple, or impression, in the middle. With both thumbs and one of forefingers, steadily press downward in center to make a hole in the clay that’s roughly 1/2 to 1/4 in. from the bottom. Periodically stop the wheel and check the depth by poking through the floor of the pot with a needle tool until the desired thickness is reached.

5. Now use forefingers or thumbs (whatever’s more comfortable) to open floor of pot outward, being sure to slide fingers across the clay STEADILY, at the same level as the desired thickness of the floor of the pot. Continue to open the clay outward until the inside diameter of the pot is roughly 10% wider than the desired inside diameter of the finished piece, to plan for shrinkage.

6. Begin to pull clay upward with fingers or knuckles of both hands, one on the outside, the other inside. First undercut the bottom edge of the pot with outside fingertip to form a clay ledge. (Always make sure to re-set the rim of the pot after each movement, to keep it on center.) With fingers of inside hand slightly higher than those on the outside and outside fingers (or knuckle) positioned underneath the clay ledge, gently squeeze the clay between the fingers at an even pressure, and steadily pull upward at the same rate the wheel is revolving. (At this stage, the wheel should revolve at a medium to slow speed.)

7. Repeat the process until the clay walls have reached an even thickness and desired height. If you accidentally knock the clay off center or end up with walls that are uneven, try this: apply a straight-edge wooden rib to the outside of the pot, and hold your left forefinger at a 90 degree angle, pointed downward, on the inside of the pot. Slowly spin the wheel and force the wall of clay between the inside forefinger and outside straight edge back into a uniform thickness, slowly and steadily gliding upward until entire wall is uniform.

8. Gently shape the pot with fingers or ribs, re-set the rim, and release from the bat with a wire or string cutter.

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WHAT ARE CERAMICS?

Ceramics are objects made of materials that are permanently hardened by being heated. Usually, the word is used to mean articles made of various forms of clay. Sticky clay is dug from the Earth and needs to have impurities, such as stones, removed before it can be used. The clay may be naturally red, yellow, grey or almost white, but can be coloured before shaping or covered with a coloured glaze.

Ceramics are essential for our day to day life. It is useful from clay products to porcelain. Generally, a ceramic is a non-metallic, solid inorganic compound. Earlier ceramics were used only for pottery. Now, with the changing times, ceramics are more and more used only for specific purposes. Use of ceramics has been from ancient times. Based on these uses there are three basic types of ceramics:

Stoneware

Stoneware is an umbrella term for ceramics fired at a higher temperature. It is known for being impermeable and hard so it’s not easily scratched. It is typically glazed. Modern brands such as Far & Away have really brought this type of ceramic back into the mix.

Clay products

In this category, many of the common ceramics like bricks and tiles are used. They are basically prepared from clay. For their shape and state, they are processed and pressed in a wet plastic state after which they are dried and then fried. Clay products that have higher density show better mechanical properties but they also have the low insulating capacity. And thus can easily catch fire. Higher density is achieved through an increase in nitrifications and also through increasing fire temperature and finer original particle size.

Refractories

Ceramic can resist higher temperatures and that is why they are also used as refractories. Refractor ceramics can withstand very high temperature and are thus used as insulating materials. They can also resist high stress. Refractors should also resist abrasive particles, hot gasses, and molten metals. For best refractors ceramics made of pure oxide is used. But these are very expensive and thus compounds made out of ceramics are used more often.

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HOW DOES A LOUDSPEAKER PRODUCE SOUND?

A loudspeaker works like a reversed microphone. Electric current flows into a coil of wire, turning it into an electromagnet. This attracts the coil to another magnet inside the loudspeaker, causing the coil to vibrate. This vibrates a diaphragm at the same frequency as the original sound, pushing air in front of it to carry the sound to the ears of the listeners. Many loudspeakers can be connected together, so that sound is heard all around a large outdoor or indoor space.

A loudspeakers (loud-speaker or speaker) is an electroacoustic transducer which converts an electrical audio signal into a corresponding sound.

A loudspeaker consists of paper or plastic moulded into a cone shape called ‘diaphragm.’ When an audio signal is applied to the loudspeaker’s voice coil suspended in a circular gap between the poles of a permanent magnet, the coil moves rapidly back and forth due to Faraday’s law of induction. This causes the diaphragm attached to the coil to move back and forth, pushing on the air to create sound waves.

Voice coil, usually made of copper wire, is glued to the back of the diaphragm. When a sound signal passes through the voice coil, a magnetic field is produced around the coil causing the diaphragm to vibrate. The larger the magnet and voice coil, the greater the power and efficiency of the loudspeaker.

The coil is oriented co-axially inside the gap; the outside of the gap being one pole and the centre post (called as the pole piece) being the other. The gap establishes a concentrated magnetic field between the two poles of the permanent magnet. The pole piece and backplate are often a single piece, called the pole plate.

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HOW DO MICROPHONES WORK?

Inside a microphone is a metal disc, called a diaphragm. When a sound wave hits the sensitive diaphragm, it makes it vibrate at the same frequency. This causes a wire coil, beneath the diaphragm, to move up and down. As the coil comes near to a magnet below, it creates a pulse of electric current in the wire. The pattern of these pulses matches the pattern of the sound wave. The pulses can be sent along a wire to a loudspeaker, to be turned back into sound, or they can be recorded on a tape or compact disc.

When you speak, sound waves created by your voice carry energy toward the microphone. Remember that sound we can hear is energy carried by vibrations in the air. Inside the microphone, the diaphragm (much smaller than you’d find in a loudspeaker and usually made of very thin plastic) moves back and forth when the sound waves hit it. The coil, attached to the diaphragm, moves back and forth as well.

The permanent magnet produces a magnetic field that cuts through the coil. As the coil moves back and forth through the magnetic field, an electric current flows through it.

The electric current flows out from the microphone to an amplifier or sound recording device. Hey presto, you’ve converted your original sound into electricity! By using this current to drive sound recording equipment, you can effectively store the sound forever more. Or you could amplify (boost the size of) the current and then feed it into a loudspeaker, turning the electricity back into much louder sound. That’s how PA (personal address) systems, electric guitar amplifiers, and rock concert amplifiers work.

Dynamic microphones are just ordinary microphones that use diaphragms, magnets, and coils. Condenser microphones work a slightly different way by using a diaphragm to move the metal plates of a capacitor (an electric-charge storing device) and generate a current that way. Most microphones are omnidirectional, which means they pick up sound equally well from any direction. If you’re recording something like a TV news reporter in a noisy environment, or a rare bird tweeting in a distant hedgerow, you’re better off using a unidirectional microphone that picks up sound from one specific direction. Microphones described as cardioid and hypercardioid pick up sounds in a kind of “heart-shaped” (that’s what cardioid means) pattern, gathering more sound from one direction than another. As their name suggests, you can target shotgun microphones so they pick up sounds from a very specific location because they are highly directional. Wireless microphones use radio transmitters to send their signals to and from an amplifier or other audio equipment (that’s why they’re often called “radio mics”).

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HOW DOES A COMPACT DISC WORK?

A compact disc (CD) has a plastic surface on which sounds are stored in binary code as very small holes, called pits, and flat areas, called lands. These can be “read” by a laser beam. The laser beam scans across the surface of the disc. When the light falls on a pit, it is scattered, but when it falls on a land, it is reflected back to a light-sensitive detector. This in turn causes a pulse of current to pass to a loudspeaker, which converts it back into sound.

If you have read the HowStuffWorks article How CDs Work, you know that the basic idea behind data storage on a normal CD is simple. The surface of the CD contains one long spiral track of data. Along the track, there are flat reflective areas and non-reflective bumps. A flat reflective area represents a binary 1, while a non-reflective bump represents a binary 0. The CD drive shines a laser at the surface of the CD and can detect the reflective areas and the bumps by the amount of laser light they reflect. The drive converts the reflections into 1s and 0s to read digital data from the disc. See How CDs Work for more information.

Normal CDs cannot be modified — they are read-only devices. A CD-R disc needs to allow the drive to write data onto the disc. For a CD-R disk to work there must be a way for a laser to create a non-reflective area on the disc. A CD-R disc therefore has an extra layer that the laser can modify. This extra layer is a greenish dye. In a normal CD, you have a plastic substrate covered with a reflective aluminum or gold layer. In a CD-R, you have a plastic substrate, a dye layer and a reflective gold layer. On a new CD-R disc, the entire surface of the disc is reflective — the laser can shine through the dye and reflect off the gold layer.

When you write data to a CD-R, the writing laser (which is much more powerful than the reading laser) heats up the dye layer and changes its transparency. The change in the dye creates the equivalent of a non-reflective bump. This is a permanent change, and both CD and CD-R drives can read the modified dye as a bump later on.

It turns out that the dye is fairly sensitive to light — it has to be in order for a laser to modify it quickly. Therefore, you want to avoid exposing CD-R discs to sunlight.

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WHO INVENTED THE GRAMOPHONE?

In 1888, the German-American inventor Emile Berliner (1851-1929) invented a system of sound recording that could be mass produced. He devised a flat disc, called a gramophone record. On the disc, a groove ran in a spiral from the outer edge of the disc to the centre. Side-to-side, rather than up-and-down movements of the stylus recorded and played the sound vibrations. Once one disc had been made, it could be used as a mould to make a metal die, which could then stamp out exact copies of the disc in large numbers.

Early attempts to design a consumer sound or music playing gadget began in 1877. That year, Thomas Edison invented his tinfoil phonograph, which played recorded sounds from round cylinders. Unfortunately, the sound quality on the phonograph was bad and each recording only lasted for only one play.

Edison’s phonograph was followed by Alexander Graham Bell’s graphophone. The graphophone used wax cylinders, which could be played many times. However, each cylinder had to be recorded separately, making the mass reproduction of the same music or sounds impossible with the graphophone.

On November 8, 1887, Emile Berliner, a German immigrant working in Washington D.C., patented a successful system for sound recording. Berliner was the first inventor to stop recording on cylinders and start recording on flat disks or records.

The first records were made of glass. They were then made using zinc and eventually plastic. A spiral groove with sound information was etched into the flat record. To play sounds and music, the record was rotated on the gramophone. The “arm” of the gramophone held a needle that read the grooves in the record by vibration and transmitted the information to the gramophone speaker.

Berliner’s disks (records) were the first sound recordings that could be mass-produced by creating master recordings from which molds were made. From each mold, hundreds of disks were pressed.

Berliner founded “The Gramophone Company” to mass manufacture his sound disks (records) as well as the gramophone that played them. To help promote his gramophone system, Berliner did a couple of things. First, he persuaded popular artists to record their music using his system. Two famous artists who signed early on with Berliner’s company were Enrico Caruso and Dame Nellie Melba. The second smart marketing move Berliner made came in 1908 when he used Francis Barraud’s painting of “His Master’s Voice” as his company’s official trademark.

Berliner later sold the licensing rights to his patent for the gramophone and method of making records to the Victor Talking Machine Company (RCA), which later made the gramophone a successful product in the United States. Meanwhile, Berliner continued doing business in other countries. He founded the Berliner Gram-o-phone Company in Canada, the Deutsche Gramophone in Germany and the U.K based Gramophone Co., Ltd.

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