The addition of lead(II) oxide into silicate glass lowers the melting point and viscosity of the melt.
After the deaths of Alfred Bell in 1895 and John Richard Clayton in 1913, the firm continued under Bell's son, John Clement Bell (1860-1944), then underneath Reginald Otto Bell (1884-1950) and lastly Michael Farrar-Bell (1911-1993) until his loss of life.