The Blaschkas used a mixture of clear and colored glass, sometimes supported with wire, to produce their models. Many pieces were painted by Rudolf. In order to represent plants which were not native to the Dresden area, father and son studied foreign plant collections at Pillnitz Palace and the Dresden Botanical Garden. They also grew some from seeds sent from the United States. In 1892, Rudolf was sent on a trip to the Caribbean and the U.S. to study additional plants, making extensive drawings and notes. At this point, the number of glass models sent annually to Harvard was approximately 120.