The Teas of commerce are subject to three principal forms of adulteration, viz.: Facing or coloring with deleterious compounds in order to enhance their appearance, mixing with spurious and spent or once used leaves, with the object of increasing their bulk, and sanding or adulterating with mineral matter to add to their weight. But it is against the two first most commonly dangerous forms of adulteration that the principal efforts of dealers and Tea inspectors should more particularly be directed, the latter having received some attention from analysts and chemists, but not to that extent which the importance of the subject merits.

Of the various forms of adulteration practiced in China and Japan, the facing or artificial coloring of low-grade Green Teas is perhaps the most prevalent and glaring, the material used for the purpose being usually composed of Prussian blue, China clay, gypsum, turmeric and indigo.

The process of coloring Green Teas is performed by placing a portion of the Prussian blue in a large bowl and crushing it into a fine powder, a small quantity of gypsum is then added, and the two substances ground and mixed together in the proportions of one part blue to four parts of the gypsum, both making in combination a light blue preparation, in which state it is applied to the leaves during the last process of firing. One ounce of this coloring matter will face or color from fifteen to twenty pounds of Tea leaves, imparting to them a dull leaden-blue color and a greasy appearance readily detected in the hand.

When Green or Japan Teas are heavily coated in this manner it may be readily recognized by their heavy leaden-blue color and oily or greasy appearance in the hand; or, better still, by placing a small sample of the leaves on a piece of glass and allowing them to rest there for some minutes, then on removing them the coloring matter, if any, will be found adhering to the glass, and its nature, whether Prussian blue, indigo or soapstone, detected by the aid of a small microscope. But when only lightly colored the best method is to put the leaves in a cup or glass and pour boiling water on them, stirring them up well meantime and then straining the infusion through a thin muslin cloth, and the coloring matter will be found deposited in the cloth or forming a sediment at the bottom or sides of the vessel into which they are strained.

What are known to trade as “Made Teas,” that is, Teas artificially manufactured from leaves once used, or tea dust, and a preparation of gum or glue to hold them together, and then colored and glazed to give them a pleasing appearance to the eye, are best detected by crushing the so-called leaves between the fingers or hands upon which they leave a yellowish stain, greasy in nature if spurious leaves. Or again, by pulverizing a small quantity of the alleged Tea leaves, and putting them in a cup or glass and pouring on boiling water, they will immediately begin to disintegrate and form a thick, gluey deposit at the bottom of the vessel, pasty in nature, the coloring matter adhering to the bottom or sides of the cup or glass.

Another form of adulteration practiced principally in China is the admixture of spurious or foreign leaves obtained from other plants, such as the willow, plum, ash, and what is known in trade as Ankoi Tea. Millions of pounds of such spurious Tea leaves are annually picked, cured and colored in the same manner as Tea in some of the Chinese Tea districts, and used for the purpose of increasing the bulk and decreasing the cost of genuine Teas, this form of adulteration, however, being only trivial when compared with the former one. Such spurious or foreign leaves in a Tea are best detected by their botanical character, that is, by the absence of the special structural marks, which distinguish the genuine Tea leaf from that of the leaves from all other plants in the vegetable kingdom, for while it is admitted that the Tea leaf bears a strong resemblance to those of the willow, plum and ash, it varies materially, however, in size, form and structure from them, the border of the true Tea leaf being more regularly serrated, the serrations stopping just short of the stalk, and the venations are very characteristic in the genuine Tea leaf, the veins running out from the mid-rib almost parallel with each other, but altering their course before the border of the leaf is reached and turning so as to leave a bare space just under it. So that in making an examination of a sample of Tea for the purpose of ascertaining whether these distinctive characteristics are present in the leaves, it will be found best to pour boiling water on to soften and uncurl them, and spread them out more easily on the glass as per the following diagrams:—

But in order to better detect the presence of spurious leaves in Tea, a better knowledge of the botanical formation of the true Tea leaf will be requisite, as Tea leaves in general bear a very strong resemblance to those of the willow, plum and ash, but vary widely in size and texture, being much smaller and more deeply serrated.

When infused and unfolded, the true or genuine Tea leaf is of a lighter-green color, the looping of the principal veinings being also very characteristic, while the spurious leaves are of a dark greenish-yellow color and very irregular in form when examined under the same conditions.

Sand and other mineral substances, such as iron and steel filings, are also frequently introduced into Tea with the object of adding to its weight, and are easiest detected by powdering a small quantity of the leaves and spreading the powder out on a piece of glass and then applying an ordinary magnet to the dust, so that if a quantity of the particles gravitate and adhere to the magnet the Tea is undoubtedly adulterated in this form.

All adulterations and fabrications in general, however, may be best detected by the following simple but effectual method: By putting a small sample of the Tea leaves in a wine-glass or thin goblet and pouring in clear cold water on them, and then stirring up or shaking well for a few minutes so that the Tea, if pure, will only slightly color the water, but if adulterated in any form a dark, muddy-looking liquor is quickly yielded, which, if next boiled and allowed to stand until cold, will, if spurious leaves are contained, become very bitter to the taste and almost transparent as it cools, while if the sample is composed of pure Tea only, it will be dark in color and pleasing in flavor under the same conditions.