DELFT, a city of the circle of Rotterdam, in the Netherlands, situated on the river Schie. It is the seat of the engineer, artillery, and marine schools, and is a naval arsenal. It is a regular, well-built city, intersected with canals, and containing seven churches, one of them with a tower three hundred feet in height. There is also the palace in which William, first prince of Orange, was assassinated in 1584; and in the churches are monuments to Van Tromp and to Grotius. There are manufactories of cloths, kerseys, and baizes, of the earthenware whose name originated from the city, of geneva, and of heavy iron goods, such as anchors and cannon. It contains 4870 houses, and 12,900 inhabitants. It is in long. 4. 16. 25. E. and lat. 52. 0. 49. N.

Delft Isle, or Cmv Island, a small island off the northwest coast of Ceylon, seven miles in length by three and a half in average breadth, and affording good pasturage for horses. It is included in the collectorship of Jaffna-patam. Long. 79. 46. E. Lat. 9. 35. N.

Delft Ware, a kind of pottery of baked earth, covered with an enamel or white glazing, which gives it the appearance and neatness of porcelain. Some kinds of this enamelled pottery differ from others, either in their sustaining sudden heat without breaking, or in the beauty and regularity of their forms, enamel, and the painting [7:7:683] with which they are ornamented. In general, the fine and beautifully enamelled potteries, which approach the nearest to porcelain in external appearance, are, at the same time, those which least resist a brisk fire; whilst those which sustain a sudden heat are coarse, and resemble common pottery.

The basis of this pottery is clay, which, when too fat, is mixed with such a quantity of sand that the earth preserves enough of its ductility to be easily worked, moulded, and turned; and yet so that its fatness may be sufficiently counteracted, and that it may not crack or shrink too much in drying or in baking. Vessels formed of this earth must be dried very gently, to avoid cracking. They are then placed in a furnace to receive a slight baking, which is only meant to give them a certain consistence or hardness. And, lastly, they are covered with an enamel or glazing, which is done by putting upon the vessels thus prepared the enamel, which has been ground very fine, and diluted with water.

As vessels to which the enamel is applied are but slightly baked, they readily imbibe the water in which the enamel is suspended, and a layer of the enamel adheres to their surface. These vessels may then be painted with colours composed of metallic calces, mixed and ground with a fusible glass. When they have become perfectly dry, they are placed in the furnace, included in cases of baked earth called seggers, and exposed to a heat capable of fusing uniformly the enamel which covers them. This heat applied to fuse the enamel being much stronger than that which was applied at first to give some consistence to the ware, is also the heat necessary to complete the baking thereof. The furnace and colours used for painting this ware are the same as those employed for porcelain. The glazing, which is nothing but white enamel, ought to be so opaque as not to show the ware under it. There are many receipts for making these enamels; but all of them are composed of sand or flints, vitrifying salts, calx of lead, and calx of tin; and the sand must be perfectly vitrified, so as to form a glass considerably fusible. Somewhat less than an equal part of alkaline salt, or twice its weight of calx of lead, is requisite to effect such vitrifications of sand. The calx of tin is not intended to be vitrified, but to give a white opaque colour to the mass; and one part of it is added to three or four parts of all the other ingredients taken together. From these general principles various enamels may be made to suit the different kinds of earths. To make the enamel, lead and tin are calcined together with a strong fire; and the sand is also made into a fritt with the salt or ashes. The whole is then well mixed and ground together, and the matter is placed under the furnace, where it is melted and vitrified during the baking of the ware. It is next ground in a mill, and applied as above directed.

The preparation of the white enamel is a very essential article in making delft ware, and one in which many artists fail. A French writer, in a memoir concerning this kind of ware, recommends the following proportions, namely, a hundred pounds of calx of lead to be mixed with about a seventh part of that quantity of calx of tin for common delft ware, or a fourth part of calx of tin for the finest kind, a hundred or a hundred and ten pounds of fine sand, and about twenty or thirty pounds of sea-salt. Concerning the earth of which the ware is made, he observes, that pure clay is not a proper material when used alone; and that different kinds of earth mixed together are found to succeed better. Pieces of ware made of clay alone are found to require too much time to dry; and they, besides, crack, and lose their form, unless they are made exceedingly thick. An addition of marl diminishes the contraction of the clay, renders it less compact, and allows the water to escape, without altering the form of the ware in drying; and it also affords a better ground for the enamel, which appears more glossy and white than when laid upon clay alone. The kinds of clay which are chiefly used in the composition of delft ware, are the blue and the green. A mixture of blue clay and marl would not be sufficiently solid, and would be apt to scale, unless it were exposed to a fire more intense than that which is commonly used for the burning of delft-ware. But to give greater solidity, there is added some red clay, which, on account of its ferruginous matter, possesses the requisite binding quality. The proportions of these ingredients vary in different works, according to the different qualities of the earths employed. Three parts of blue clay, two parts of red clay, and five parts of marl, form the composition used in several manufactories. M. d’Antic thinks that the best delft ware might be made of equal parts of pure clay and pure calcareous earth; but this composition would require that the fire should be continued twice as long as it generally is.