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In 1789, he invented a new kind of earthenware with a lead-free glaze for the tableware production, the so-called Vienna ware. In 1810, he invented an artificial pumice and years later, a version of stoneware which was used to make mortars, funnels and other utensils. A flexible, unbreakable blackboard was also produced.
In 1792, Hardtmuth established a pencil factory in Vienna after he succeeded in creating an artificial graphite pencil by mixing powdered graphite with clay. Until that time, whole pieces, cut from graphite, were glued in between wood and were imported from England. With the new method, graphite of inferior quality could be used in pencil manufacturing, lowering the price and making the product more accessible for the masses. His company Koh-i-Noor Hardtmuth still exists.