In January, 1918, the Brick and Clay Record published an article on the Vitreous Clay Package Company of Ohio. It is a fascinating piece of American history, both for marble collectors and historians in general. Not only is it fascinating, but also it is quite an obscure bit of history, at least as measured by Google search results, for a search for "Vitreous Clay Package Company" yields only two or three results.
With so many American men still fighting "Kaiser Bill" overseas in World War I, labor was short. Imports of German marbles were blocked, making demand higher than ever. To meet that demand for marbles and other clay products, the Vitreous Clay Package Company employed women in a factory that could make up to five million glazed marbles and sixty thousand clay bottles per week.
In addition to photos of the actual factory and some of its equipment, the article goes on to describe in detail some of the methods used. I only wish they had printed close-up photos of the marbles themselves. I have to assume they were not thinking of the needs of marble collectors almost 100 years into the future!