This is performed with verifiable colours, that is to say, mixed with fluxes which generally vitrify at a low temperature. It is a very easy process, much us0d in pottery, and also by amateurs, but it gives rather dull effects, which are far from being equal to the decoration "au grand feu".

Substances used.

Chinese While.

Persian White.

Light Blue.

Dark Blue.

Persian Blue.

Turquoise Blue

Dark Brown.

Red-brown

Light Yellow.

Dark Yellow.

Black.

Rose (Pink).

Bed.

Violet.

Remarks.

Flux(1)..

(2)

(7)

..

85

(5)

80

(9)

(3)

(5)

(5)

(4)

(7)

(2)

10

(1) The flux is prepared with:

White clay...

..

..

..

(4)

10

(4)

..

..

..

..

..

..

..

(4)

(4)

flint.................70

Carbonate of soda . . 10

Armenian bole...

..

..

..

..

..

..

..

10

..

..

..

..

..

..

..

" of potash................... 15

Calcine...

..

..

..

..

..

..

..

..

20

55

..

..

..

..

..

Minium....................................... 5

Thiviers sandstone...

..

...

..

..

..

..

..

..

..

..

..

..

10

..

..

Mix with care melt, and grind.

Crushed porcelain...

..

30

..

..

..

..

..

..

..

..

..

..

..

..

..

(2) Grind together:

Persian white.................. ...20

Glaze of „ . .

..

...

..

..

30

80

..

..

..

..

..

..

..

..

..

Stanniferous white enamel.. 40

Nevers sand..

..

20

..

..

...

..

..

..

..

15

..

..

..

..

..

(3) Grind together without melting.

Flint.....

..

..

..

..

...

..

...

..

..

..

30

20

..

30

..

Aluminium (oxide) .

..

..

..

..

..

..

..

..

..

5

6

2

..

5

..

Alumina.

Antimony " ...

..

..

..

..

..

..

..

..

4.5

73

22

..

..

20

..

..

..

..

..

..

..

..

..

0.8

..

..

..

..

...

..

Sal ammonate.

..

10

..

..

..

...

..

..

..

..

..

35

..

...

..

Chalk.

..

..

..

..

..

..

..

..

..

..

..

..

..

..

(4) To be melted.

,, (nitrate).

...

..

(8)

..

..

..

..

..

..

..

..

..

..

..

..

(5) Mix and bake ina crucible under the kiln during a firing.

" (oxide)..

..

..

...

50

5

..

..

..

..

..

7

..

..

..

2

(6) Grind together, fire, wash, and crash.

Copper (oxide)...

..

..

..

..

..

..

..

..

..

..

15

..

..

50

..

tin (oxide)...

..

..

..

..

..

..

..

..

..

..

..

80

..

..

...

Stannic acid.

Iron (chromate). . .

..

..

..

..

..

..

40

..

..

..

20

..

..

30

...

(7) precipitate with the ammonia in a solution in water of 12k. alum and 9k. of nitrate of cobalt,filter, dry, and calcine au grand feu.

„ (oxide) .

..

...

..

..

..

..

..

..

..

41

35

..

..

10

...

„ (sulphate) .

..

..

..

..

..

..

20

..

..

..

..

..

..

...

Manganese (oxide)

..

..

..

..

..

..

15

..

..

..

..

..

..

55

Lead (protoxide)

..

..

..

..

..

..

..

..

..

..

..

..

...

..

Litharge.

,, (plumbate)

..

..

...

35

..

10

..

2.5

6.5

50

44

..

2.5

40

30

Minium.

Potassium (bichromate)

..

..

..

..

..

...

..

..

..

..

4

..

..

(8) The mixture is heated for some hours at a bright red heat, then ground and washed in water acidulated with HCl.

„ (nitrate)

..

...

..

...

..

...

..

...

..

..

...

..

..

10

Soda (borate) .

..

..

..

...

..

..

..

...

..

..

4

..

..

..

Melted borax

Zinc (oxide)

...

...

...

..

40

...

25

..

..

16

...

..

..

...

..

Florwers of zinc

The verifiable colours are obtained ready prepared in commerce. A large number of French (Poulenc freres, Lavoisier, etc.) and foreign firms supply them of excellent quality. It is only the great pottery factories which make them themselves.

The application is made with the brush, the colours being diluted with essence and oil. Sometimes the pottery is coated with resin dissolved in an essence or in oil, and is then powdered over with the dry colour.

In the trade line-engraving is used for monochrome designs, and chromolithographic printing for polychrome decoration.

The design, having been traced in outline with lithographic ink, is printed off in the ordinary way, on to as many stones as there are to be colours; the parts of each stone which are to be coloured are coated with a brush with lithographic ink; the remainder of the design is effaced, and the stones are placed in acidulated water to fix the ink and give it a slight relief.

The parts of the stone coated with ink are varnished by means of a wooden roller covered with leather, and a proof is taken off upon paper sized with gum or dextrine. The paper when taken off is turned over and sprinkled with a verifiable colour which sticks to the varnish; after drying the excess of colour is removed with a soft brush and the second colour is printed, great care being taken in fitting the sheet in its place. The process is thus continued until all the colours have been applied. To remove them to the piece of pottery, the prepared sheet of paper is covered with a varnish, and applied to it with a pad; when the varnish has adhered, the whole is plunged into water to remove the paper, is then dried, heated in the stove to remove the varnish, glazed, and fired.

This process, which gives good results with flowers and ornaments, is not so successful in reproducing animals or figures. We must then turn to photolithography, a process in which the sketch is replaced by a photograph; this is transformed into an engraving, which can be reproduced by printing, for instance, by means of the bichromate gelatine.

The firing is carried out at a rather low temperature in special muffled kilns (p. 449).