Glazing signifies the coating or enamelling of earthen ware with any vitreous substance, the barfs of which consists of lead. It is one of those familiar arts with which the ancients were doubtless better acquainted than our modern potters. The Roman urns discovered in Yorkshire, instead of being glazed, are covered on both sides with a fine varnish of a red coral tint, smooth, beautiful, and incomparably more durable than all our earthen vessels; having withstood the effects of time for a long series of centuries.
On the contrary, the glazing of all our earthen ware is very apt to crack, both from moisture and heat, being composed of lead, one of the most pernicious metals that could be devised for such important purpose. It is well known that lead is easily volatized by heat, and readily decomposed by any vegetable acid : hence it has been affirmed by various eminent writers, that we are under the necessity of inhaling or swallowing, perhaps every day, a minute portion of a metal which is one of the slowest, but most destructive poisons, and lays the foundation of many fatal disorders, such as palsy, dry colic,consumption, etc. the remote cause of which has not, till lately, been suspected.
Although we are no advocates for spreading alarm, or exciting apprehension, yet there appears to be sufficient reason to believe that our glazed culinary vessels are a latent source of disease; and when fruit or acids be allowed to remain in them for some time, the liquors or substances thus preserved will necessarily acquire a very dangerous impregnation from the metal.
Instead, therefore, of describing the composition and process by which earthen vessels are usually glazed, we shall earnestly recommend various substitutes for lead to the attention of the public.
M. Westkumb, an eminent German chemist, was required by the government- of Hanover to devise a less pernicious method of glazing earthen ware than - was hitherto practised. In consequence of numerous experiments, he has at length published the successful result of several compositions, in in which not a particle of lead was employed, and which in his opinion will prove an useful glazing for ordinary vessels.
Another method of glazing with-out lead has been invented by M. Nieseman, a potter at Leipzig : it consists of half a pound of saltpetre, half a pound of pot-ash, and one pound of common salt. This composition is not very expensive, and said to produce an enamel not inferior to that prepared with lead. Professor Leonhardi has investigated, and found it eminently useful. We trust, therefore, our pot-ters will in future conscientiously desist from using that pernicious and slowly poisonous metal.