The best bird-lime is made of the middle bark of the holly, boiled seven or eight hours in water, and, when soft, it is laid in pits in the ground, and covered with stones, and left to ferment till it is reduced to a kind of mucilage. It is afterwards kneaded till it is freed from extraneous matter, and then washed in a running stream till no impurities appear. In this state it is left four or five days in earthen vessels to ferment and purify itself, when it is fit for use. It may likewise be obtained from the misletoe, young shoots of elder, and other vegetable substances. It is sometime's adulterated with turpentine, oil, vinegar, and other matters. Good bird-lime is of a greenish colour, and sour flavour; gluey, stringy, and tenacious; and, in smell, resembling linseed oil.