A sulphide refers to a white clay figure that was inserted into molten glass. The insertion was done by hand and the quality of each sulphide marble was greatly affected by the skill of its maker. The artisan has to try to center the figure as best he could, and the clay figure had to be heated to the same temperature as the glass or the marble would crack or shatter during the process. Additionally, the maker needed just enough air to be trapped around the clay figure to give it its signature silvery sheen but too much air would obscure the viewing of the figure with a reflection when the marble was finished.
The sulphide process was originally developed in France and subsequently improved upon in England for items such as buttons, paperweights, and tableware. The marbles were almost exclusively made in Germany, though there are thought to be rare examples from the United States made during the Victorian period.