419. China and Glass.--The best material for cleansing either porcelain or glass, is fuller's earth: but it must be beaten into a fine powder, and carefully cleared from all rough or hard particles, which might endanger the polish of the surface.
420. In Cleaning porcelain, it must also be observed that some species require more care and attention than others, as every person has observed that china-ware in common use frequently loses some of its colours.
421. The Red, especially of vermilion, is the first to go, because that colour, together with some others, is laid on by the Chinese after burning.
422. The Modern Chinese Porcelain is not, indeed, so susceptible of this rubbing or wearing off, as vegetable reds are now used by them instead of the mineral colour.
423. It ought to be taken for granted that all china or glass ware is well tempered: yet a little careful attention may not be misplaced, even on that point; for though ornamental china or glass-ware is not exposed to the action of hot water in common domestic use, yet it may be injudiciously immersed therein for the purpose of cleaning; and as articles intended solely for ornament are not so highly annealed as others, it will be proper never to apply water beyond a tepid temperature.
424. An ingenious and simple mode of annealing glass has been some time in use by chemists. It consists in immersing the vessel in cold water, gradually heated to the boiling point, and suffered to remain till cold, when it will be fit for use. Should the glass be exposed to a higher temperature than that of boiling water, it will be necessary to immerse it in oil.