| Arab | Italian | |
|---|---|---|
| Copper sulphide | 26.87 | 24.74 |
| Silver sulphide | 1.15 | 1.03 |
| Mercury sulphide | — | 24.74 |
| Red ocher | 71.98 | 49.49 |
These were ground with vinegar and applied with the brush to the already baked enamel. A great variety of iridescent and metallic tones can be obtained by one or the other, or a mixture of the following formulas:
| I | II | III | IV | V | VI | |
|---|---|---|---|---|---|---|
| Copper carbonate | 30 | — | — | 28 | — | 95 |
| Copper oxalate | — | — | — | — | 5 | — |
| Copper sulphide | — | 20 | — | — | — | — |
| Silver carbonate | — | 3 | — | 2 | 1 | 5 |
| Bismuth subnitrate | — | 12 | — | — | 10 | — |
| Stannous oxide | — | — | 25 | — | — | — |
| Red ocher | 70 | 85 | 55 | 70 | 84 | — |
Silver chloride and yellow ocher may be respectively substituted for silver carbonate and red ocher. The ingredients, ground with a little gum tragacanth and water, are applied with a brush to enamels melting about 1814° F., and are furnaced at 1202° F. in a reducing atmosphere. After cooling the ferruginous deposit is rubbed off, and the colors thus brought out.
Sulphur, free or combined, is not necessary, cinnabar has no action, ocher may be dispensed with, and any organic gummy matter may be used instead of vinegar, and broom is not needed in the furnace. The intensity and tone of the iridescence depend on the duration of the reduction, and the nature of the enamel. Enamels containing a coloring base—copper, iron, antimony, nickel—especially in presence of tin, give the best results.
To Toughen China.
How To Tell Pottery And Porcelain.
CHEESE
Manufacture.
“The acid indispensable to the coagulation of milk is not added to the milk in the preparation of cheese, but it is formed in the milk at the expense of the milk-sugar present. A small quantity of water is left in contact with a small quantity of a calf’s stomach for a few hours, or for a night; the water absorbs so minute a portion of the mucous membrane as to be scarcely ponderable; this is mixed with milk; its state of transformation is communicated (and this is a most important circumstance) not to the cheese, but to the milk-sugar, the elements of which transpose themselves into lactic acid, which neutralizes the alkalies, and thus causes the separation of the cheese. By means of litmus paper the process may be followed and observed through all its stages; the alkaline reaction of the milk ceases as soon as the coagulation begins. If the cheese is not immediately separated from the whey, the formation of lactic acid continues, the fluid turns acid, and the cheese itself passes into a state of decomposition.