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雅思阅读真题+题目+答案:Dyes and Pigments

来源:原创作品 | 2019-11-2221

雅思阅读真题+题目+答案:DyesandPigmentsADyeingisaprocessofcolouringmaterials,orclothfibers,wherebythecolourbecomespartofthefiber.Thefastnessofthecolour,oritspermanency,dependsupont...

雅思阅读真题+题目+答案:Dyes and Pigments

A

Dyeing is a process of colouring materials, or cloth fibers, whereby the colour becomes part of the fiber. The fastness of the colour, or its permanency, depends upon the dye and the process used.丁rue dyeing is a permanent colour change, and the dye is absorbed by, or chemically combined with, the fiber.

B

In ancient times all the dyes used were natural; actually, this was true up until mid-1800. The dyestuffs came from a variety of natural sources, some commonly available, others rare or difficult to produce. Some of the common dyes included logwood or quercitron, fustic, woad, and indigo. An example of the rare dyes would be cochineal and Tyrian purple. Collectively, these substances are called dyestuffs,and were occasionally traded as a commodity. The dyestuffs were extracts from plants, mollusks, insects, woods, or naturally occurring minerals. There are many plants which produce dye suitable in the dyeing process, and many were heavily cultivated. Madder and woad were grown in Europe specifically for their dyeing properties. Saffron was also extensively grown in Anatolia for its yellow dye. Probably one of the most famous dyes was Tyrian purple,from a Mediterranean shellfish. The Phoenicians of Tyre,in Lebanon, produced this very expensive dye long before written history began. Many other areas had special dyes which were famous in antiquity.

c

The value of a dye is not just its availability, but also its fastness or durability against daily use. It must withstand washing, wearing, sunlight, perspiration, without losing 在n appreciable amount of its colour. The colour, and its bright1ess, also helped determine the dye’s value. Premium colours were purple, blue, and bright shades of red.

D

There are two classifications of dyeing, the home craft and the trade, or industrial, dyeing. The manufacturing of clothing, the spinning, weaving and embroidery,tended to stay within the family unit. An exception to this would be the carpets made in Anatolia and Persia, for example, or the very fine, sheer linen woven in Egypt. But the manufacture of dyes and their use in dyeing yam and cloth soon became an industry, supporting large numbers of people, even entire cities. The art of dyeing was one of the earliest arts known to man after he became civilised. Trade dyeing was, however, a highly competitive business. These were the professionals of the ancient world when it came to dyed cloth. Many of the processes were closely guarded secrets, and many of the special skills were handed down over generations. The ingredients may come from far away; the tools may be specialised and the process often was steeped in superstition.

E

As far back as man can historically see, rulers have set themselves apart from everyone else by wearing exotic and rare items, and dyed clothing was very fearly a part of this status proclamation. Still today the important and the wealthy prefer to wear items not available to all. In Egypt, the pharaohs wore specially made clothing, dyed with colours difficult to obtain. Dyed fabrics from tombs of early Egyptian attest to the antiquity of the dyers art.

F

In the ancient Greek and Roman world, Tyrian purple became the colour of choice for rulers and emperors. The dye was extremely expensive, therefore, available to only a few. When in later times merchants, considered unimportant, became wealthy enough to buy purple-dyed cloth. Laws were passed to prevent their diluting the impressiveness of the colour. Only rulers, or emperors, were allowed to wear purple. Later, however, the law was changed to include the rulers' family; then senators; and so on, eventually losing its status. This is where the phrase “born to the purple" came from.

G

The word pigment comes from the Latin “pigmentum” meaning coloured material. Pigments are generally distinguished from dyes as colouring materials on the basis of their soluble ability (solubility) characteristics. Pigments are used mainly in the colouration of paints, printing inks and plastics, although they are used to a certain extent in a much wider range of applications including textiles, ceramics, paper, and cosmetics. In contrast to dyes, pigments are highly insoluble colouring materials, which are incorporated into an applications medium by dispersion, and they remain as discrete solid particles held mechanically within a polymeric matrix. Pigments are thus required to resist dissolving in solvents, which they may contact in application to minimise problems such as “bleeding” and migration. In addition to solvent resistance, pigments are required to be fast to light, weathering, heat and chemicals such as acids and alkalis to a degree dependent on the demands of particular application.

H

Natural inorganic pigments, derived mainly from mineral sources, have been used as colourants since prehistoric times and a few, notably iron oxides, remain of some significance today. The origins of the synthetic inorganic pigment industry may be traced to the introduction of Prussian blue in the early 18th century,pre-dating the synthetic organic colourant industry by some 150 years. The organic pigments are the oxides, sulfides, hydroxides, silicate, sulfates and carbonates of metals. The colour of a pigment is due to its interactions with light by scattering and absorption.

I

The synthetic organic pigment industry emerged towards the end of the 19th century out of the established synthetic textile dyestuffs industry. Many of the earliest organic pigment were known as “lakes” These products were prepared from established water soluble dyes by precipitation on to an insoluble inorganic substrate. A further significant early development in organic pigments was the introduction of a range of azo pigments. One of the most critical events in the development of the organic pigment industry was the discovery, in 1928, of copper phthalocyanine blue. This was the first pigment to offer the outstanding intensity and brightness of colour typical of organic pigments combined with an excellence range of fastness properties, comparable with many inorganic pigments. Organic pigments generally provide higher intensity and brightness of colour than inorganic pigments. However, organic pigments are unable to provide the degree of opacity offered by most inorganic pigments which have the lower reflectance.


雅思阅读真题题目:

Question 1-7

Choose the most suitable headings for paragraphs A-G from the list of headings below.

write appropriate numbers (i-xi) in boxes 1-7 on your answer sheet.

NB There are more headings than paragraphs, so you will not use them all.

Question 1-7

Choose the most suitable headings for paragraphs A-G from the list of headings below.

Write appropriate numbers (i-xi) in boxes 1-7 on your answer sheet.

NB There are more headings than paragraphs, so you will not use them all.

List of Headings

I Clothing symbolising status

II The factors determining the dye’s quality

III The invaluable colour

IV The importance of plants in ancient times

V From family to industry

VI The value of colours

VII Dyestuff sources in the past

VIII Availability and durability of a dye

IX The competitive and secret industry

X Pigments, insoluble colouring materials

XI The definition of dyeing



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