By HENRY ADKINS.
RED LEAD, which forms one of the principal ingredients in the composition of flint glass, has been for a considerable period extensively manufactured in Birmingham and several of the adjacent towns. The invention of flint glass, which is of English origin, arose out of the difficulties experienced in the use of coal as fuel. To protect the glass from the injurious effects of the smoke produced by the imperfect combustion of this substance, it was found necessary to make use of covered pots, which increased the difficulty of fluxing the materials to such an extent as to render necessary the addition of some other ingredient to increase the fusibility of the glass. This object was accomplished by the use of oxide of lead. The brilliancy of the glass thus produced, the facility with which it could be worked by the glassblower, on account of its easy fusibility, and the readiness with which it could be ornamented by the glasscutter, on account of its softness, have caused the continuance of its use, although the obstacles which at first impeded the manufacture of glass without lead have since been overcome, and a flint glass, containing but a small quantity of lead, is now extensively manufactured at Newcastle-on-Tyne.
The principal supply of glassmakers' red lead was at one time obtained from Derbyshire. The quality was inferior, and imparted to the glass an objectionable shade of colour, known in the trade as Derbyshire blue. This defect was afterwards remedied by Messrs. Blair and Stephenson, of Tipton, who secured for many years a monopoly of the supply of the finest quality.
About the year 1817, Mr. Boyle, who had been for some time manager of the works of the above-named firm, entered into partnership with Messrs. Adkins and Nock, of Smethwick, who a few years later commenced the manufacture of glassmakers' red lead, and, on the retirement of Messrs. Stephenson and Co. from the trade, became fo some years the principal makers.
In the course of time several new firms entered the trade, which is now extensively carried on in many parts of the country; nevertheless, the manufacturers of the midland district still maintain their pre-eminence, and the principal supply of the best quality consumed in the United Kingdom is produced in the above-named locality.
The process of manufacture is as follows:— A quantity of lead is placed on the bed of a reverberatory furnace, of a peculiar construction, and exposed to a high temperature, while the metal is constantly agitated by striking it upon the surface with a rake. A combination takes place between the lead and the oxygen of the atmosphere, and the oxide of lead thus formed is removed by the rake to the back of the furnace. These operations are continued during a period of twelve hours, at the expiration of which time any metallic lead which may have failed to have become oxydised (sic) is removed, and the remaining oxide is exposed, by constant turning, to the action of the air, and, at the termination of a further period of twelve hours, is withdrawn from the furnace. The substance thus produced, which is called litharge, is now ground into an impalpable powder with water, and flows into a series of tubs, where it is kept in a state of agitation by a revolving stirrer, furnished with arms. The particles of metal which have escaped oxidation, having a greater specific gravity than the oxide, remain in the stirring tubs, while the oxide of lead passes on to another series of tubs, where it subsides from the water. The supernatent (sic) water is afterwards removed by a syphon, and the moist litharge transferred to a reverberatory furnace, where it is exposed to the combined action of a low temperature and a current of air for a period of twenty-four hours. During this process, the litharge enters into combination with a further quantity of oxygen, and minium, or red lead, is produced. The manufacture is completed by passing the substance through a revolving cylinder or wire gauze, to remove any lumps that may have formed, or any large particles of foreign matter with which it may have become intermixed during the previous operations.
The principal manufacturers in this district are Messrs. T. Adkins and Co., Smethwick; Messrs. Lloyd and Co., Smethwick; and Messrs. Burr Brothers, Shrewsbury.