Steel, an alloy based on iron and carbon. Although they were once tin-plated to protect against corrosion, modern "tin" cans contain little or no tin.

The purity of the gold. One carat is one twenty-fourth, by weight, so 24 carat gold is basically pure gold. 14 carat gold is 58% gold, and 42% other metals. 24 carat gold would be too soft and easily worn away for a precious object.

Because it contains copper. Gold is mixed, or "alloyed," with other metals to make it stronger, but most additions are white metals, like silver, and these quickly remove the yellow color of gold. You can make "white gold" this way, for example. The yellow color is restored by adding copper.

Ice. Ice is used for structures such as igloos or bridges, and was even proposed as a means of making aircraft carriers in the Second World War. It can be used right up to its melting point. Most other materials soften considerably below their melting point, and lose structural rigidity.

Aluminum. When the monument was topped off, in 1885, aluminum was one of the most expensive materials in the world, and a small pyramid of it was used on top of the obelisk. In 1886, Hall and Heroult announced a new process for the extraction of aluminum from its ore, and the price dropped to the point where the metal became an everyday commodity.

Expansion on freezing. Most materials contract when they freeze into a solid form, but water expands when it freezes, so ice is less dense than liquid water, and it floats. Without this unusual property, the iceberg would not have been on the sea surface, to sink the Titanic. Silicon shares this property.

China.

No. Crystalline material is characterized by atoms or molecules that are lined up in ordered arrays. Crystalware, or "lead crystal" is really a form of glass, in which the atoms are almost as randomly placed as in a liquid.

Because black paint dried faster than any other color, and so speeded the production of the cars. Allowing the paint to dry was the slowest part of the entire production line.

When the Paris landmark was constructed in 1887, steel was a new "wonder material" but wrought iron was cheaper, and architect Gustave Eiffel was more familiar with its properties. He went with what he knew, and although the tower was intended to be a temporary exhibit for the 1889 International Exhibition, it has certainly stood the test of time.

It is one of many decorative iron pillars found in India. It was made in about 310 AD and exhibits an unusual resistance to corrosion, having stood apparently in one place with no sign of rusting after nearly 2,000 years.

The supermarket! Some checkout bar-code scanners have windows made of artificial sapphire, because ordinary glass would become scratched by the constant passage of groceries over its surface. Unlike gem sapphire, artificial sapphire is nearly colorless.

Joseph Stalin. Originally Ioseb Dzhugashvili, he named himself after the Russian "Stal" or "Steel." Steel production was the most significant measure of national prowess at the time.

Herbert Hoover. He also translated a classic metallurgical textbook from its original Latin into English.

American 5-cent coins are made of an alloy of copper and nickel. Pure nickel would be too hard to be struck into coin using a forging die.

It is named after the Devil ("Old Nick"). Saxon miners often came across a reddish rock that they mistook for copper ore, but despite their best efforts they could not extract a drop of copper from it. They attributed their failure to a copper devil who had taken up residence in the ore and refused to allow extraction of the copper. The ore actually contained nickel, which was successfully extracted centuries later.

Mostly zinc. Copper has become so expensive that there is a risk that it might cost more than a penny to make a penny! Modern one-cent coins are a sandwich of zinc between two thin layers of copper.

Church roofs were made of lead, and the ore they were produced from was often contaminated with silver. In 1833 H. L. Pattinson invented a process that allowed silver to be extracted from lead, and church roofs became a primary source of silver. A church roof would be removed, have its silver extracted and be replaced in return for the silver it produced.

Not really - even if you actually could! Atomic scale defects called "dislocations" are places where the regular arrangement of atoms in the steel structure of the car is disturbed. If the steel contained no dislocations it would be very weak and easily bent by hand.

The city-state of Venice made it a crime punishable by death to reveal the secrets of glassmaking. Glass was the source of most of the city's wealth.

Tin. This metal deforms by a relatively unusual process called "twinning" which involves the propagation of waves through the metal at the speed of sound. If you bend a piece of pure tin between your fingers it makes a sound like a cat mewing.

Alan Heeger, Alan MacDiarmid and Hideki Shirakawa, three materials scientists who developed electrically conductive polymers. Other materials science winners of the Nobel Prize include William Shockley, John Bardeen and Walter Brattain who shared the Physics prize in 1956 for discovering the transistor

At a town called Iron Bridge, near Coalbrookdale, in England. The use of coal to make wrought iron in this district, in about 1713, is widely regarded as marking the start of the Industrial Revolution.

When molten glass cools, it does not solidify like other materials; it just gets progressively more and more viscous. Glass has no crystalline structure, and can be considered to be a supercooled liquid. Contributed by Stephanie Rothrauf

Originally, Teflon didn't stick very well - you had to use special utensils so the Teflon didn't chip off. Today, the pan's surface is roughened by being sandblasting. A primer is applied to the surface and then the Teflon is embedded in the primer. The Teflon won't chemically bond to anything else, but you can mechanically get it stuck in microscopic cracks and crevasses. Contributed by Stephanie Rothrauf

The guiness Book of World Records lists Teflon as the slipperiest substance on Earth. Its invention was an accident. In 1938, a scientist at DuPont, Dr. Roy Plunkett, made the first Teflon. He was investigating different gases in an attempt to come up with a better coolant. Plunkett left one batch of this gas overnight in a container. When he came back the next day, the gas was no longer there. Instead, the container held a waxy solid, which he found to be very slippery and impervious to all sorts of corrosive chemicals. This was called polytetrafluoroethylene (PTFE), a solid version of the fluorocarbons (freon), which later became known as Teflon. Contributed by Stephanie Rothrauf

The Bronze Age. Bronze is an alloy (or mixture) of copper and tin, and is stronger than either of them is alone. Contributed by John Hammond

A bowling ball. It is made of one long polymer chain. Contributed by John Hammond

250 pounds. In the 1960's, the average automobile contained only 50 pounds of aluminum. The major advantage of aluminum is its light weight, which improves fuel economy. The amount of aluminum used in a car reflects a balance between the demands of increasing the fuel economy, and keeping the sticker-price low. Aluminum costs about four times as much, per pound, as steel, but its usage in cars is constantly increasing. Contributed by Sean Weber

Stainless Steel. In Sheffield, England, during 1912, Harry Brearley was trying to develop a new alloy for gun barrels for the British Army. He threw out samples that didn't meet the requirements and later discovered a shiny piece of metal amidst all the rusty ones in the rain-soaked scrap-heap. That sample was an iron-chromium alloy that is the basis of all stainless steel used today. (It is still not used for gun barrels.)

Leonid Brezhnev. Before becoming the Soviet Leader in 1964, he was the director of the Dneproderzhinsk Metallurgical Technical College.

Gadolinium, atomic number 64, a silvery metal discovered in 1880 by J.C. Galissard de Marignac, and named after J. Gadolin, a Finnish chemist. Gadolinium is used in high-strength magnets for recording heads.

Genghis Khan. His parents gave him the name Temujin, meaning "iron worker." "Genghis Khan" is an honorary title that he adopted later probably meaning something like "warrior king."

Concrete. From about 800 to 1300AD essentially no concrete was used for construction, though many ancient concrete structures are still standing today. Modern concrete, based on Portland cement, dates back only to 1756.