Oxides uncombined with other substances, are not susceptible of fusion, in order to promote which, a flux is added; the composition of which, varies according to the means or medium employed for diluting the colours at the time they are used. Where a volatile oil is used for diluting, a flux composed of glass, nitre and borax is proper; but where gum water is employed the compound must be of glass, lead and silex. A flux is the medium of attachment of the colour to the porcelain under the action of fire, as oil or water were previously in painting.

Parts of.

The Fluxes are No. 1. Red Lead............ 8

Calcined Borax ... 1 1/2

Flint Powder ...... 2

Mint Glass ......... 6

No. 2. Flint Glass......... 10

White Arsenic...... 1

Nitre.................. 1

No. 3. Red Lead............ 1

Flint Glass ......... 3

No. 4. Red Lead........... 9 1/2

Uncalcined Borax.. 5 1/25

Flint Glass ......... 8

A

No. 5. Flint Glass ......... 6

Flux No. 2 ......... 4

Bed Lead............ 8

N.B

The ingredients of these fluxes are melted together, and then finely pounded for use. At Sevres the following flux is sometimes used.

Powdered Glass.................................40

Calcined Borax .................................22

Refined Nitre....................................44

The ingredients must be as pure as possible, and the smallest particle of lead must not be admitted. Triturate the former in a glass mortar for an hour, and then expose them in a crucible, on a charcoal fire, until the swelling of the fused mass ceases.

It is only by these fluxes, that the oxides or colours are fixed upon porcelain, as, by being enveloped in the flux, they are preserved from the action of the air, and retain their brilliancy.

If too little flux be used, the colours will be dull. If too much, they will run, and destroy delicacy and precision of outline. Colours which require for their fusion six times their quantity of flux, are unfitted for the finer portions of porcelain painting.

Certain colours require various proportions of fluxes.

The general rule is five parts of flux to two of colouring matter.

Colours when required for use, should be pounded in an agate, glass or porcelain mortar, covered to prevent the intrusion of dust, etc. They must be afterwards ground on a glazed palette, perfectly level, and firmly fixed in plaster on a wooden frame, but these precautions are only necessary for the manufacturer, not for the artist, who receives his materials subsequent to these troublesome processes.

In like manner it is the duty of the potter to attend to the evaporation of the oil used as a diluent, before the painted porcelain is placed in the enamelling kiln.

(Dilding, it may be observed, is performed with or without a flux, as the gold will adhere to the surface by the incipient fusion of the other materials.

When japanner's gold size is used it is moistened to the required degree with one of the volatile oils. When the size has so far dried, as only to be clammy, the gold leaf is laid on with cotton wool on a row of fine hairs like a comb. It is desirable, as soon as possible, to place the gilded porcelain in the oven or muffle. The oxygen of the gold is drawn off, and the intense heat cements the metal to the porcelain.