The Coloration and Glazing of the Teas of Commerce

Art. VIII.- ?The Coloration and Glazing of the Teas of Commerce. By R.Warrington,F.C.S. (The Quarterly Journal of the Chemical Society, No. xiv. 1851. Art. xv. P. 156.) In the year 1839, on the 16th of August, a Report on the Manufacture of Teas in China and the kingdom of Assam was published by Mr C. A. Bruce ; and in this report, which was soon after republished in the Edinburgh New Philosophical Journal, it was stated that the articles used in glazing and colouring various forms of the green teas especially, was indigo, with sulphate of lime.1 It appears now, according to the results of positive analysis by Mr Warrington, that this colour never is communicated by means of indigo, but by another article much less costly, namely, Prussian blue or prussiate of iron. Mr Warrington shewed in a former communication to the Chemical Society in February 1844, that there are two kinds of green tea, known in commerce as the glazed and the unglazed; that the glazed is coloured by the Chinese with a mixture of Prussian blue and gypsum, or sulphate of lime, to which a yellow vegetable colouring matter is sometimes added; that the unglazed kinds are merely dusted with a small quantity of gypsum powder ; and that in the specimen of what is called Canton gunpowder this glazing or facing is carried to the highest degree. Mr Warrington then also stated, that he had never met with a sample of green tea, in which the blue tint was given by means of indigo. Since the date of the publication of that paper Mr Warrington has received from various parties of experience much additional information, which may be interesting upon an article in such general dietetic use. It was stated in the report by Mr Bruce, that the Chinese call the former (the indigo) Youngtin; the latter, the sulphate of lime, Acco. According to Mr J. Reeves, one of the authorities of Mr Warrington, this is a mistake. Indigo, he believes, is never employed for colouring tea ; and the term 1 Edinburgh New Phi!. Journal, October 1339, vol. xxviii. 18 40. P. 126. 374 Mr R. Warrington on the Youngtin, as used by Mr Bruce, should be Yong-teen, that is, foreign blue, the name given by the Chinese to Prussian blue, in contradistinction to Too-teen, native blue, or indigo. Another doubt was thrown upon the inferences drawn by Mr Warrington. Mr Fortune, in his work on China, says of the used in dyeing the northern green teas for ingredients " foreign markets (p. 201), There is a vegetable dye obtained from Isatis indigotica, much used in the northern districts, and called Tein-ching, and it is not unlikely that it may be the substance which is employed." Again, at page 307, Mr " Fortune says, I am very much inclined to believe that this, the Tein-ching, is the dye used to colour the green teas which are manufactured in the north of China for the English and American markets.'' This question Mr Warrington thinks is now settled, and the experimental evidence he had adduced, placed beyond doubt, by positive demonstration. Mr Fortune forwarded from the north of China for the Industrial Exhibition spe- cimens of these materials, which, from their appearance, are undoubtedly fibrous gypsum calcined, turmeric root, andPrus- sian blue ; the latter of a bright pale tint, most likely from admixture with alumina or porcelain clay. Alumina and silica were found in the former analysis, and their presence was attributed to the possible employment of kaolin or agal- matolite. Mr J. R. Reeves, in a letter to Mr Thompson, dated 1st July 1844, says, "Mr Warrington's experiments have led him to correct results as to the substances used, which I know to be Prussian blue, fibrous gypsum, and turmeric ; the second being sulphate of lime; and the last the yellow or orange- coloured vegetable substance mentioned by Mr W., but not named. The colouring is not intended as an adulteration ; it is given to suit the fancy of foreign buyers, who judge of an article used as a drink by the eye, instead of the palate. You well know how little the London dealers like the yel- lowish appearance of uncoloured green tea. The Americans a few years ago carried the dislike farther than the English ; and therefore the Chinese merchant had scarcely any chance of selling his tea unless he give it a face which would suit them. The small quantity of colouring matter used must preclude the idea of adulteration as a source of profit. Mr J. Reeves states, that in the East India Company's time, gypsum and Prussian blue were sometimes used upon hyson teas ; Tien Hing using the first, on his pale bright hyson; Lum Hing the latter, on his dark bright leaf. But these were Coloration and Glazing of the Teas of Commerce. 375 only in minute quantities, just sufficient to produce a uniform face. The gypsum in its calcined state is used, Mr Warrington thinks, for the purpose of absorbing moisture, and enabling the tea the better to withstand the damp of the sea voyage. Mr Warrington received from Dr Royle, since his last communication, a sample of green tea from the Kemaon District in the Himalayas, which is quite free from facing; and the green teas of Java are likewise without this covering. On Black and Green Teas. Though the distinct preparation of green and black tea from the respective plants, the Thea, viridis and the Tliea Bohea, has been warmly advocated by many botanists, yet it is now generally admitted by all parties, that green and black teas can be and are made, indiscriminately from the same parcel of leaves, taken from the same species of plant. It is nevertheless, well known to all persons, that the infu- sions from these teas have marked differences in colour and flavour, and that the effects produced in certain constitutions by green tea, such as nervous irritability, sleeplessness, &c. are very different from those arising from the use of black tea. Their characteristic physical differences are well known ; but they possess peculiar chemical properties to be noticed im- mediately, and which have always been ascribed by chemists to the effect of high temperature in the process of manufacture. To explain these pecularities, Mr Warrington directs atten- tion to certain changes which take place in herbs and vegetable substances dried in different modes. From observations made upon various substances of this kind, in the routine work of the establishment, to which Mr Warrington is attached, especially the exsiccation of medicinal herbs, he had been led to form certain inferences as to changes taking place in these articles. These herbs are for the most part nitrogenous plants, as Atropa belladonna, Hyoscyamus niger, Conium maculatum, and others. The plants are brought to the establishment by the growers or collectors from the country, tied up in bundles, and when they arrive fresh and cool, they dry of a good bright green colour; but on the contrary, it is found, that if they are delayed in their transit, or remain in a confined state for too long a period, they become heated, from a species of spontaneous fermentation, and when loosen- ed and spread open, they emit vapours and are sensibly warm to the hand. When such plants are dried, the whole of the 376 Mr It. Warrington on the green colour is found to have been destroyed; and a red- brown and sometimes a blackish-brown tint is the result. Mr "Warrington also noticed, that a clear infusion of such leaves, evaporated carefully to dryness, was not all undissolved by water, but left a quantity of brown oxidized extractive matter, to which the denomination of Apothene has been applied by some chemists. A similar result is obtained by the evaporation of an infusion of black tea. The same action takes place upon the exposure of the in- fusions of many vegetable substances to the oxidizing influ- ence of the atmosphere. They become darkened on the sur- face ; and this gradually spreads through the solution, and on evaporation, the same oxidized extractive matter will remain insoluble in water. Mr Warrington further found that the green teas when wetted and re-dried, with exposure to the air, were nearly as dark in colour as the ordinary black teas. From these observations, therefore, MrWarrington wasled to form the conclusion, that the peculiar characters and chemical differences which distinguish black tea from green, were to be attributed to a species of heating and fermentation accompanied with oxi- dation by exposure to the air, and not to its being submitted to a high temperature in the process of drying, as has been generally believed. This opinion received some confirmation by ascertaining from parties conversant with the Chinese manufacture, that the leaves for the black teas were always allowed to remain exposed to the air, in mass, for some time before they were roasted. Mr Ball, in his work on the manufacture of tea,1 has de- scribed in detail the whole series of these processes, fully confirming the opinion previously formed by MrWarrington. Some of these facts had been published in Batavia in 1844. by Mr Jacobson in the Dutch language.2 In the preface to " his work Mr Ball says : It will be seen by dates incidentally adverted to, that the facts and most of the materials of this work, were established and collected thirty years " ago."? These facts, as well as other materials, were derived from conversation with growers and manipulators from the tea districts; from written documents furnished by Chinese; from published works in the same language diligently sought out; and also from correspondence with a Spanish mission- ary long resident in the province of Fokim.

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