My Science School

Plate glass is thick, good quality glass made in huge sheets for shop windows. It’s very smooth surface is made by floating the molten glass onto a bath of molten tin. Tin melts at a lower temperature than glass, so the glass begins to set on the tin and is then passed over rollers as it finishes cooling. The larger the bath of molten tin the larger the glass that can be made.

Plate glass, flat glass or sheet glass is a type of glass, initially produced in plane form, commonly used for windows, glass doors, transparent walls, and windscreens. For modern architectural and automotive applications, the flat glass is sometimes bent after production of the plane sheet. Flat glass stands in contrast to container glass (used for bottles, jars, cups) and glass fiber (used for thermal insulation, in fiberglass composites, and optical communication).

Flat glass has a higher magnesium oxide and sodium oxide content than container glass, and lower silica, calcium oxide, and aluminum oxide content. (From the lower soluble oxide content comes the better chemical durability of container glass against water, which is required especially for storage of beverages and food). Most flat glass is soda-lime glass, produced by the float glass process (1950s). Other processes for making flat glass include:

Scratches can occur on sheet glass from accidental causes. In glass trade terminology these include “block reek” produced in polishing, “runner-cut” or “over/under grind” caused by edge grinding, or a “sleek” or hairline scratch, as well as “crush” or “rub” on the surface.

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Slip is a mixture of clay and water, forming a thick liquid. It can be used as a kind of glue to stick a handle onto a cup when both are “leather hard” (hard enough to handle but still soft enough to cut with a knife). Slip can also be poured into plaster moulds to form intricate shapes. The plaster absorbs water from the slip, causing it to dry on the outside first. If the rest of the slip is poured away, hollow vessels and ornaments can be made.

In pottery, pieces of clay sometimes need to be joined to each other.  A handle on a cup for example.  The way this is done is by scoring (scratching marks in) the edges that need to be joined, thereby creating a key.  Then liquefied clay is pasted onto the two edges before pressing them together.  This creates a bond.

The liquefied clay is called slip.  Sometimes the words slip and slurry are used interchangeably.  However, it is also argued that technically slip is thinner than slurry.  And that slurry is actually the particular kind of thick, gloopy slip that is used for bonding pieces of clay.

Generally, slurry that is used for joining pieces of pottery consists only of particles of the clay being used in the pot itself suspended in water.  This is important because different kinds of clay shrink and vitrify at different rates.  If you join pieces of clay together with slurry that has a different shrink or drying rate to the pot itself, the join may not be very strong.

There is no particular hard and fast ratio for clay to water for joining clay.  How liquid the slip needs to be depends on how wet your clay pieces are.  If the clay is still relatively wet the slip does not need to be too thick.  However, when the clay has begun to dry out, then the slip needs to be thicker in order for the pieces to key into one another.

Slip for joining clay is sometimes called ‘joining slip’.  It can be bought or made.  However, it is a good idea for the slip to be have the same clay body as the pot itself.  Therefore, it is often recommended that the potter makes the slip themselves.

Slip is also used to decorate items of pottery.  The term engobe is used to describe a clay slip coating that is applied to the body itself.  This can either improve the texture of the item or add color. Engobe is opaque and can be white or colored.  Colored engobe usually contains stains and metal oxides.

Engobe is different from slip in that it has lower clay content than slip.  It also contains more silica and flux than regular slip.  This means it shrinks less than slip when it dries.

Some people claim that engobe is half way between being a slip and a glaze.  Fired engobe surfaces have a bit of a sheen that fired slip surfaces do not have.  Others, state that engobe and glaze are quite different.  They point out that if an engobe creates too much of a glazed effect, it loses its opacity, which is its most important property.

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In the heat of the kiln, glaze would fuse with the shelf that the object stands on, so glaze is carefully wiped from the base of the object before it is fired.

In lower temperature firings, like cone 06–04, you can use a stilt, which is a small piece of ceramic material with pointed wires sticking out of it. You fire the pot sitting on the pointed wires. This leaves small marks in the glaze which sometimes have to be cleaned up a bit. In higher temperature firings such as cone 10, it’s not practical to glaze the bottom of a vase. The norm is to have what is called a dry foot where no glaze is applied to the bottom. A stain or a colored slip can be applied to the foot before firing if there’s too much contrast between the color of the bare ceramic and glazed areas. It’s also possible to construct a foot ring on the bottom of the vase in such a way that the glaze can at least be applied to the edge of the bottom without sticking the pot to the shelf. That does add a level of difficulty, though, since glaze can move during the firing, and you need to leave a little distance between the shelf and the glaze in case it does move. On my pots, I don’t attempt to do that, but accept the look of the dry foot.

The pot has to stand on something (or hang from something, with its own problems) during firing. It cannot float. During firing, the glaze melts. If you have glaze on the bottom of the pot, when the glaze cools it sets solid and fixes the pot to the kiln shelf or floor. Even if you can get the pot off the shelf, probably taking bits of shelf with it, you will have to grind down the rough bits. More likely the pot will break during cooling as the pot contracts more than the shelf, with (very sharp, beware) bits left stuck to the shelf and the pot ruined (also the shelf). If you can find a way to make pots float, then you can glaze the bottom.

You can hang them, but you need a suitable hanging point, and you may not want to have a hanging hole in your pot, and if you do, that part will have to be unglazed, so there will always be an unglazed part. And some plates appear to have completely glazed bases with no unglazed bits, but if you look carefully, you find breaks in the glaze between base and rim, where the plate has been supported during firing.

There has to be a break in the glaze where the ware is supported, it doesn’t have to be on the bottom, but if it isn’t it will be somewhere else, probably more visible.

Many items have an indented bottom which is glazed, leaving just a thin ring unglazed. Some potters like to do this as to them it looks more professional; others don’t, preferring the handmade look of a bare base. Many factories glaze the base this way, but there is still always an unglazed ring. It has to stand on something during firing!

Glass is an extraordinarily useful material. The substances from which it is made are easy to find and very cheap. Glass is mainly melted, cooled sand, but other ingredients are added, such as sodium carbonate (soda ash) and limestone. Although it appears solid to us, glass is in fact a liquid, flowing incredibly slowly. When windows that are hundreds of years old are measured, they are found to be slightly thicker at the bottom than at the top, as the glass very gradually flows downwards.

In a commercial glass plant, sand is mixed with waste glass (from recycling collections), soda ash (sodium carbonate), and limestone (calcium carbonate) and heated in a furnace. The soda reduces the sand's melting point, which helps to save energy during manufacture, but it has an unfortunate drawback: it produces a kind of glass that would dissolve in water! The limestone is added to stop that happening. The end-product is called soda-lime-silica glass. It's the ordinary glass we can see all around us.

Once the sand is melted, it is either poured into molds to make bottles, glasses, and other containers, or "floated" (poured on top of a big vat of molten tin metal) to make perfectly flat sheets of glass for windows. Unusual glass containers are still sometimes made by "blowing" them. A "gob" (lump) of molten glass is wrapped around an open pipe, which is slowly rotated. Air is blown through the pipe's open end, causing the glass to blow up like a balloon. With skillful blowing and turning, all kinds of amazing shapes can be made.

Glass makers use a slightly different process depending on the type of glass they want to make. Usually, other chemicals are added to change the appearance or properties of the finished glass. For example, iron and chromium-based chemicals are added to the molten sand to make green-tinted glass. Oven-proof borosilicate glass (widely sold under the trademark PYREX®) is made by adding boron oxide to the molten mixture. Adding lead oxide makes a fine crystal glass that can be cut more easily; highly prized cut lead crystal sparkles with color as it refracts (bends) the light passing through it. Some special types of glass are made by a different manufacturing process. Bulletproof glass is made from a sandwich or laminate of multiple layers of glass and plastic bonded together. Toughened glass used in car windshields is made by cooling molten glass very quickly to make it much harder. Stained (colored) glass is made by adding metallic compounds to glass while it is molten; different metals give the separate segments of glass their different colors.

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Ceramics are baked to make them hard and waterproof. Until they are baked (fired) ceramics can be mixed with water again to form clay. Firing is done in a large oven called a kiln. In large ceramics factories, the kilns are heated all the time. They are like long tunnels, through which ceramics move slowly on trolleys in a never-ending process. The first firing that a clay article receives is called a biscuit firing. It makes the article hard and brittle, but it is still porous. Water can be absorbed by it.

Firing clay transforms it from its humble, soft beginnings into a new, durable substance: ceramic. Ceramics are tough and strong and similar in some ways to stone. Pieces of pottery have survived for thousands of years, all because clay met fire.

The temperature needed to transform soft clay into hard ceramic is extremely high and is usually provided by a kiln. You cannot fire pottery in a home oven because ovens do not get up to the high temperatures of more than 1,500 degrees Fahrenheit that you need for firing clay.

Firing is the process of bringing clay and glazes up to a high temperature. The final aim is to heat the object to the point that the clay and glazes are "mature"—that is, that they have reached their optimal level of melting. To the human eye, pots and other clay objects do not look melted; the melting that occurs is on the molecular level.

Bisque firing refers to the first time newly shaped clay pots, or greenware, go through high-temperature heating. It is done to vitrify, which means, "to turn it glasslike," to a point that the pottery can have a glaze adhere to the surface.

Greenware is fragile. To start, it must be bone-dry. Then, it must be loaded into the kiln with a great deal of care. The kiln is closed and heating slowly begins.

Slow temperature rise is critical. During the beginning of the bisque firing, the last of the atmospheric water is driven out of the clay. If it is heated too quickly, the water turns into steam while inside the clay body, which can cause the clay to burst.

When a kiln reaches about 660 degrees Fahrenheit, the chemically bonded water will begin to be driven off. By the time the clay reaches 930 degrees Fahrenheit, the clay becomes completely dehydrated. At this point, the clay is changed forever; it is now a ceramic material.

The bisque firing continues until the kiln reaches about 1730 degrees Fahrenheit. At this temperature, the pot has sintered, which means it has been transformed to the point that it is less fragile while remaining porous enough to accept the application of glazes.

After the desired temperature has been reached, the kiln is turned off. The cooling is slow to avoid breaking the pots due to stress from the temperature change. After the kiln is completely cool, it is opened and the newly created “bisque ware” is removed.

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There are many ways of decorating pots. They can be dipped in a glaze, made of tiny particles of glass in a liquid, and fired for a second time. The glassy covering melts onto the pottery, making it completely waterproof. Pottery can also be decorated after glazing, with transfers, hand-painted designs, or by screen-printing. It may then be fired for a third time to fix the decoration.

Glazes are the most often used form of pottery decoration. They come in a huge variety, including nearly every color imaginable and many types of textures. Glazing can transform a simple pot into something really special and the techniques you can use are endless. On a practical level glazes are used to make a pot vitreous and both food and liquid safe. When a piece has been bisque fired and then put through a separate glaze firing, it makes the pot much more durable. Raw glazed work tends to flake off more easily and you won't get this problem with a separate glaze firing.

Glazes can be laid on top of each other to create even more effects. This is called overglazing. Some "overglazes" are simply other glazes that are applied on top of another unfired glaze that will mature at the same temperature. True overglazes may also be applied after the base glaze has already been fired. These overglazes will require the ware to go through a third firing, at a lower temperature than the base glaze.

Underglazes are not glazes themselves but are colorants applied to unfired bisqueware (greenware) before an overglaze is applied (usually the overglaze is transparent to really let the colors of the underglaze shine through). Underglazes provide the flexibility for a huge range of creativity. Firstly, there's the range of colors you can use, as you can mix the underglazes to get your perfect shade. With underglazes, you have the opportunity to paint your own detailed designs and patterns. You can even use the underglazes like watercolors, as when you're painting straight onto a rough clay surface, there's less chance of the glazes slipping.

Slips and engobes are essentially the same thing. The difference in term is basically a difference in regional language preference. “Slip” is more common in Europe, and “engobe” is more common in North America. Both words refer to a liquid slurry consisting of clay or clay mixed with coloring agents. Slips and engobes are used to decorate wet greenware, adding color, texture, or two-dimensional design. The advantages of using an engobe are that you can use them for raw (or single) firing, meaning you can apply them to work when it is still slightly damp or even leather hard. Unlike, glassy glazes, engobes usually produce a matt surface rather than a glossy shine. The exception to engobes being matt in texture is terra sigillata, which can be buffed to have a higher shine to it.

Clay is a master chameleon. With skill, clay can successfully visually mimic all sorts of substances, from metal to old shoes. Clay is impressionable. Textures can readily be added to wet pots through impressing a variety of tools and objects into the surface.

Clay is also carve-able. Marks and designs can be incised into leather-hard greenware. By doing so at the leather-hard stage of drying, the cuts retain their crispness. Leather-hard greenware also allows for more ease when incising more intricate patterns.

Marbling with two different types of clay—say, a white clay body and a terracotta (or alternatively a colored clay)—is a wonderful way to create different effects on your pottery. One of the best ways to do it is to roll out the two different colors of clay into sheets, then stack them on top of each other. Then start gently rolling the whole block. The colors will mix together and make the most beautiful marbled patterns and from there you can hand build or use a mold to create your desired shape.

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Clay can be used to make a huge variety of ceramic articles, from tiny electronic components to bricks and baths. It is a good insulator and, when covered with a glaze, is completely waterproof. Unlike many metals, glazed clay is unreactive, so that acidic foods will not stain it, and exposure to water and the air will not tarnish or corrode it.

Clay is made from the slow chemical weathering of silicate bearing rocks like granite and feldspar and other igneous rock. Usually the weathering is from it is slightly acidic solution other times it is geothermal. It becomes a hydrolyzed aluminum phyllosillicate. Al2Si2O5 (OH)4) They form flat hexagonal sheets that are less than 2 micrometers. The sheets are made of tetrahedral silicate sheets and octahedral hydroxide sheets. There are about 30 types of clay. Natural clays are always a mixture of these many types. There are primary and secondary clays. Primary ones are found where they were formed. Secondary ones have moved by water and deposited somewhere else.

Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, dishware, smoking pipes, and even musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is also used in many industrial processes, such as paper making, cement production, and chemical filtering. Until the late 20th century, bentonite clay was widely used as a mold binder in the manufacture of sand castings.

Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage (lining the landfill, preferably in combination with geotextiles). Studies in the early 21st century have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.

Medical use: A traditional use of clay as medicine goes back to prehistoric times. An example is Armenian bole, which is used to soothe an upset stomach. Some animals such as parrots and pigs ingest clay for similar reasons. Kaolin clay and attapulgite have been used as anti-diarrheal medicines.

As a building material: Clay building in South-Estonia Clay as the defining ingredient of loam is one of the oldest building materials on Earth, among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of the world's population, in both traditional societies as well as developed countries, still live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.

Also a primary ingredient in many natural building techniques, clay is used to create adobe, cob, cordwood, and rammed earth structures and building elements such as wattle and daub, clay plaster, clay render case, clay floors and clay paints and ceramic building material. Clay was used as a mortar in brick chimneys and stone walls where protected from water.

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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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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.

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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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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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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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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Discs were the main method of recording and playing music for the first half of the twentieth century, but sound recording on steel tape was used in the 1930s by radio stations. In 1935, two German companies developed a strong plastic tape, which had a layer of iron oxide on the surface. This invention eventually made it possible for smaller, domestic tape recorders to come into use. In 1963, Philips introduced something they called a “compact cassette”, which contained a thin tape within a plastic case. This was much lighter and more convenient for home use.

A cassette tape, tape cassette, or only cassette – is a rectangular and flat container that helps record & play audio and video. The original cassette tape only recorded audio, and that was enough. Usually, cassette tapes are made of plastic. But some models come with metal constructions. Cassettes have the sole purpose of transporting the magnetic tape. This is where the data comes from (sound & video signals).

These cassettes can be inserted in a recorder, so they can be used to record audio and/or video directly. And without having to handle the tape by hand – the cassette will do it automatically. When the cassette is put inside a player, then the magnetic tape will do its job to provide the audio or video from its small guides on tape. In short, a cassette tape allows users to transfer data around in magnetic tape – conveniently.

Magnetic Tape

On blank magnetic tape, the magnetized particles are all facing in the same direction. Electrical signals created by recorded sounds because the magnetized particles to move into patterns that match the sound signal. When the tape is played, the head “reads” the magnetized particles and creates electrical signals to match them, which are relayed to a loudspeaker to be played. In order to wipe the recording from the tape, all that needs to happen is for the tape to be passed through a strong magnetic field, which lines up the magnetized particles once more.

Magnetic recording, method of preserving sounds, pictures, and data in the form of electrical signals through the selective magnetization of portions of a magnetic material. The principle of magnetic recording was first demonstrated by the Danish engineer Valdemar Poulsen in 1900, when he introduced a machine called the telegraphone that recorded speech magnetically on steel wire.

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In 1877, the American inventor Thomas Edison (1847-1931) experimented with a machine called a “phonograph”, which converted sound vibrations into grooves on a cylinder covered with tinfoil. A sharp needle, called a stylus, was attached to a diaphragm at the narrow end of a large horn. When sound waves travelled into the horn, they made the diaphragm vibrate, causing the needle to move up and down, and cutting a groove of varying depth in the tinfoil. If this process was reversed, so that the needle was made to run over the grooves, it caused the diaphragm to vibrate. Vibrations passed through the horn, pushing air in front of them, to reach the listener’s ear as sound. Later, wax-coated cylinders were used instead of tinfoil, to give a better result.

The history of sound recording - which has progressed in waves, driven by the invention and commercial introduction of new technologies — can be roughly divided into four main periods:

• the “Acoustic” era, 1877 to 1925


• the “Electrical” era, 1925 to 1945


• the “Magnetic” era, 1945 to 1975


• The “Digital” era, 1975 to the present day.

Experiments of capturing sound on a recording medium for preservation and reproduction began in earnest during the Industrial Revolution of the 1800s. Many pioneering attempts to record and reproduce sound were made during the latter half of the 19th century – notably Scott’s Phonautograph of 1857 – and these efforts culminated in the invention of the phonograph by Thomos Edison in 1877. Digital recording emerged in the late 20th century and has since flourished with the popularity of digital music and online streaming services.

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