The kilns are made with either fixed or revolving retorts.
The rolled sheet is left on the castingtable until it has set sufficiently to be pushed over a flat iron plate without risk of distortion; meanwhile the table has been placed in front of the opening of one of the large annealing kilns and the slab of glass is carefully pushed into the kiln.
The ore yields about 46% of iron, and contains about 2.5% of sulphur, the roasting of the ores being necessaryore-roasting kilns are more extensively used here than in any other place in the country.
In practice the proximity to chalk pits or lime kilns, the cost of the lime and cartage, will determine which is most economical.
What then happened was very natural: imitations of the old wares were produced, and having been sufficiently disfigured by staining and other processes calculated to lend an air of rust and age, they were sold to ignorant persons, who labored under the singular yet common hallucination that the points to be looked for in specimens from early kilns were, not technical excellence, decorative tastefulness and richness of color, but dinginess, imperfections and dirt; persons who imagined, in short, that defects which they would condemn at once in new porcelains ought to be regarded as merits in old.