Sometimes paper is made heavier and more glossy (shiny) by adding clay, and by 'milling' it. Milling is done by squeezing the paper through a series of rollers. Sometimes paper is made from used or waste paper: this is recycling.
Not all paper is made from wood. Other kinds of fiber can be used. People still make paper from cotton, linen and hemp for special purposes.
Writing started long before the invention of paper. People wrote on many kinds of material. They wrote on cloth, on the stone walls and on wood. In Mesopotamia the Sumerians wrote on clay tablets, many of which have survived today. In Europe, people wrote on vellum.
Many centuries ago – as early as the 3rd millennium BC (that's over 2000 BC) – people in Egypt made a kind of paper from the papyrus plant. This is where the word 'paper' comes from. The people of Greece and Rome learned to do this too. The Romans wrote on parchment (made from animal skin), on waxed tablets and on wood (see Vindolanda).
In China 105 AD, the eunuch Cai Lun told his Emperor he had made paper. They had previously used bamboo and silk. The material used in this ancient paper included cotton rags, hemp, various plant fibres and old fish nets. The oldest existing paper with writing on it was found in the ruins of a watchtower in the Great Wall of China. It dates to about 150 AD. Even earlier paper (but with no writing on it) has been claimed: "The oldest surviving piece of paper in the world is made of hemp fibers, discovered in 1957 in a tomb near Xian, China, and dates from between the years 140 and 87 BC". Paper-making was regarded by the Chinese as so valuable that they kept it secret as long as they could.
People in Japan learned how to make paper with fibres of the mulberry tree, around 610 AD. This is called Japanese paper or "Washi". The Chinese invention spread to India, and then to the Middle East, and then to Italy.
An opportunity occurred after The Battle of Talas in 751. Then an Arab army captured soldiers of the Chinese. There were some paper makers among the captured soldiers. From them, paper-making spread throughout the Islamic world. In 757, a paper mill was built at Samarkand. People learned to use linen as paper raw material and to use starch made from flour as an additive.
The Italians used hemp and linen rags. In 1276 the first Italian paper mill was built at Fabriano and, until the 14 century, Italy was a paper supplier in Europe. In 1282 the first watermark was introduced in Bologna.
Paper was hard to make. It was cheaper than the old writing materials, but still expensive. A mechanical paper maker was conceived in France 1798, but invented in England. At least one paper mill was using them by 1812. Now the process was cheaper but the raw material was still expensive.
In 1840 Friedrich Gottlob Keller Invented a machine that could make pulp for paper out of wood fibres (instead of the expensive rag paper). Paper became cheap enough for everyone to buy. Around the same time, other inventions were made, like the pencil, the fountain pen, and a printing press that used steam power. With this new information technology, people wrote more letters, made more books and newspapers, and kept more records of what they did.
Today, some of the largest paper-producing countries are China, USA, Canada, Finland, Sweden and Russia. Paper is produced in large factories called "paper mills". They produce hundreds of thousands of tons of paper each year.
Paper is used for writing and printing. Books, magazines and newspapers are printed on paper.
Paper is often used for money. Paper used for money is made in special ways. It does not use wood fiber. It is mostly cotton with additives to make it hard for people to print their own money. A piece of paper money is called a banknote, a bill or a note.
Paper can be used for cleaning. Special forms of paper are used, such as paper towels, facial tissues or toilet paper.
Pretty paper can be used as decoration. It can be pasted onto the walls of a room; this is called wallpaper. Paper can be used to wrap gifts. This is called wrapping paper or gift wrap.
Some kinds of paper are strong and can be used in boxes and other packaging material. Sometimes several layers of paper are held together with glue, to make cardboard.
Power
Power has different meanings when talking about different subjects:
States of matter
There are four common states of matter (or "phases") in the universe: solid, liquid, gas, and plasma.
The state of matter affects a substance's properties. Examples of those properties include density, viscosity (how well it flows), malleability (how easy it is to bend), and conductivity. Changes between states of matter are often reversible.
In a "solid", the positions of atoms are fixed relative to each other over a long time. That is due to the cohesion or "friction" between molecules. This cohesion is provided by metallic, covalent or ionic bonds. Only solids can be pushed on by a force without changing shape, which means that they can be resistant to deformation. Solids also tend to be strong enough to hold their own shape in a container. Solids are generally denser than liquids. Solid becoming a gas is called sublimation.
In a "liquid", molecules are attracted to each other strongly enough to keep them in contact, but not strongly enough to hold a particular structure. The molecules can continually move with respect to each other. This means that liquids can flow smoothly, but not as smoothly as gases. Liquids will tend to take the shape of a container that they are in. Liquids are generally less dense than solids, but denser than gases.
In a "gas", the chemical bonds are not strong enough to hold atoms or molecules together, and from this a gas is a collection of independent, unbonded molecules which interact mainly by collision. Gases tend to take the shape of their container, and are less dense than both solids and liquids.
Gases have weaker forces of attraction than solids and liquids. Gas becoming a solid directly is called deposition.
Gases can sometimes turn directly into solids without passing through a fluid stage. That is called desublimation. You see it in the hoary frost which forms on window-panes in cold climates. It is the reverse of sublimation.
"Plasmas" are gases that have so much energy that electrons of an atom cannot stay in orbit around one atomic nucleus. The atomic ions and free electrons mix around like a hot soup.
Because the positive and negative charged particles are not stuck together, plasma is a good conductor of electricity. For example, air is not good at conducting electricity. However, in a bolt of lightning, the atoms in air get so much energy that they no longer can hold on to their electrons, and become a plasma for a brief time. Then an electric current is able to flow through the plasma, making the lightning.
Plasma is the most common state of matter in the universe. Both stars and the interstellar medium are mostly made of plasma.
Phases of matter can be changed by a number of things. The most common ones are temperature and pressure. Substances usually become a gas at warm temperatures and/or low pressures, become a solid at cool temperatures, and become a plasma at extremely hot temperatures. Substances often become liquid in between solid and gas, but when the pressure is very low (such as the vacuum of outer space) many substances skip the liquid phase, going directly from solid to gas or vice versa. Scientists have created graphs called phase change diagrams to show the relationship between pressure, temperature, and phase of many substances.
When a solid becomes a liquid, it is called melting. When a liquid becomes a solid, it is called freezing. When a solid becomes a gas, it is called sublimation. When a gas becomes a solid, it is called desublimation. When a liquid becomes a gas, it is called evaporation. When a gas becomes a liquid, it is called condensation.