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Hence such violent ebullition in volcanos, and hence the emission of so much pumice-stone and ashes, which are of the same nature. In the body of our whin-stone, on the contrary, there is no mark of calcination or vitrification.
He had but to cover this material with a vitrification of transparent glaze, to obtain one of the most important products of fictile art that which, under the name of English earthenware, was to attain the greatest commercial value and become of the most extensive utility.
The reader will see, in the place quoted, or in the avant-propos to his Mémoire sur les Iles Ponces, the fact to be this; That the Chevalier Dolomieu finds those bodies which we either cannot melt in our fires, or which we cannot melt without changing them by calcination and vitrification, he finds, I say, these substances had actually been melted with his lavas; he also finds those substances, which are necessarily dissipated in our fires, to have been retained in those melted mineral substances.
We must cursorily refer to some other fortifications which really scarcely belong to our subject, though certain archaeologists claim for them a prehistoric origin. We refer to the vitrified forts, which are strange structures in which stones, such as granite and gneiss, quartzite and basalt, have been subjected to a heat so intense as to produce vitrification.
Nay, the very colour of the stones, and the quantity of what bears every resemblance to vitrification, scattered about, all tend to induce the, belief that the main island owes its formation to the same cause which doubtless produced the smaller one that has now disappeared. It is not, however, to be inferred from the above description that St. Michael's is nothing but a barren rock; far from it.
Many of them retain traces of Roman. occupation. The Gueret Museum possesses a fragment from the Ribandelle walls in which a Roman tile is completely imbedded; and M. Thuot picked up other tiles in a similar condition amongst the ruins. This is a very decided proof that the vitrification took place after the arrival of the conquerors of Gaul.
This bath has for its object to remove the coating of bichromate, so as to allow the color to adhere to the glass, from which it has been separated by the layer of glucose and bichromate, which would prevent the vitrification. The bath has also for its object to render the light parts of the picture perfectly pure and capable of being easily retouched or painted by hand.
What unfortunate points of vitrification have I laid open to your fire?" "I thought they were probably forgotten by you, Sir." "I shall be exceedingly obliged to you if you will put me in condition to defend myself." "I think nothing could do that, Mr. Stackpole. Under whose auspices and fostering care was this curse of slavery laid upon America?"
Our porcelain seems to be a partial vitrification of levigated flint and fine pipe clay, mixed together in a certain proportion; and if the pieces are not removed from the fire in the very critical moment, they will be either too little, or too much vitrified.
Yet one other possible solution may be mentioned, a solution which is becoming more and more generally accepted, namely that the granite was not after all really melted, but that the vitrification should either be attributed to the fusion of the argillaceous mass, which has been subjected to an igneous transformation, such as that which often takes place in furnaces for baking bricks and in lime-kilns.
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