These were household utensils and tools made from metal: copper, tin, and iron.

In the 18th century, the Dutch used kooper (sometimes spelled koper) for both pure copper and for brass, copper containing from 5 - 15% zinc. They also used tin for both pure tin and for pewter, tin containing from 1 - 15% copper. Steel, an alloy of iron and carbon, was not common until the mid-1800's, and thus too expensive when cheaper metals and alloys would suffice. In Leeuwenhoek's time, steel was used mostly for cutting edges.