Brief history of paper
http://en.wikipedia.org/wiki/Paper
http://en.wikipedia.org/wiki/Paper_size
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets.
Paper is a versatile material with many uses. Whilst the most common is for writing and printing upon, it is also widely used as a packaging material, in many cleaning products, in a number of industrial and construction processes, and even as a food ingredient – particularly in Asian cultures.
Paper, and the pulp papermaking process, was said to be developed in China during the early 2nd century AD by theHan court eunuch Cai Lun, although the earliest archaeological fragments of paper derive from the 2nd century BC in China.
History
The oldest known archaeological fragments of the immediate precursor to modern paper date to 2nd century BC in China. Papermaking is considered one of the Four Great Inventions of China, and the pulp papermaking process is ascribed to Cai Lun, a 2nd century AD Han court eunuch. With paper an effective substitute for silk in many applications, China could export silk in greater quantity, contributing to a Golden Age.
Paper spread from China through the Middle East to medieval Europe in the 13th century, where the first water-powered paper mills were built. In the 19th century, industrial manufacture greatly lowered its cost, enabling mass exchange of information and contributing to significant cultural shifts. In 1844, Canadian inventor Charles Fenerty and German F.G. Keller independently developed processes for pulping wood fibers.
Types, thickness and weight
The thickness of paper is often measured by caliper, which is typically given in thousandths of an inch.Paper may be between 0.07 millimetres (0.0028 in) and 0.18 millimetres (0.0071 in) thick.
Paper is often characterized by weight. In the United States, the weight assigned to a paper is the weight of a ream, 500 sheets, of varying "basic sizes", before the paper is cut into the size it is sold to end customers. For example, a ream of 20 lb, 8.5 in × 11 in (216 mm × 279 mm) paper weighs 5 pounds, because it has been cut from a larger sheet into four pieces. In the United States, printing paper is generally 20 lb, 24 lb, or 32 lb at most. Cover stock is generally 68 lb, and 110 lb or more is considered card stock.
In Europe, and other regions using the ISO 216 paper sizing system, the weight is expressed in grammes per square metre (g/m2 or usually just g) of the paper. Printing paper is generally between 60 g and 120 g. Anything heavier than 160 g is considered card. The weight of a ream therefore depends on the dimensions of the paper and its thickness.
Most commercial paper sold in North America is cut to standard paper sizes based on customary units and is defined by the length and width of a sheet of paper.
The ISO 216 system used in most other countries is based on the surface area of a sheet of paper, not on a sheet's width and length. It was first adopted in Germany in 1922 and generally spread as nations adopted the metric system. The largest standard size paper is A0 (A zero), measuring one square meter (approx. 1189x841 mm). Two sheets of A1, placed upright side by side fit exactly into one sheet of A0 laid on its side. Similarly, two sheets of A2 fit into one sheet of A1 and so forth. Common sizes used in the office and the home are A4 and A3 (A3 is the size of two A4 sheets).
The density of paper ranges from 250 kg/m3 (16 lb/cu ft) for tissue paper to 1,500 kg/m3 (94 lb/cu ft) for some speciality paper. Printing paper is about 800 kg/m3 (50 lb/cu ft).
Paper may be classified into seven categories:
- Printing papers of wide variety.
- Wrapping papers for the protection of goods and merchandise. This includes wax and kraft papers.
- Writing paper suitable for stationary requirements. This includes ledger, bank, and bond paper.
- Blotting papers containing little or no size.
- Drawing papers usually with rough surfaces used by artists and designers, including cartridge paper.
- Handmade papers including most decorative papers, Ingres papers, Japanese paper and tissues, all characterized by lack of grain direction.
- Specialty papers including cigarette paper, toilet tissue, and other industrial papers.
