Lithography is a printmaking method that works on the principle of the immiscibility of oil and water. Alois Senefelder invented it in the 18th century. He drew images and wrote words but instead of etching them on metal plates, he printed them on an oil and water-affine rock. He then drew the image on the oil and water-affine rock with an accessory substance such as ink. The end of the process was fixing the image chemically. In the 19th century, lithography became more popular as intuitive ways of mass production were discovered which lowered the overall price of the prints. Honoré Daumier and Francisco Goya were socially and politically charged artists who used touchstone lithography along with affordable mass production to reach a wider audience. Their touchstone lithography works were produced during the highest peak of lithography's popularity which coincided with the birth of European political caricatures. In modern times, contemporary artists such as David Hockney continue using lithography in their works because of the unique aesthetic it offers along with its versatility. Traditional methods of lithographic printing merged with robotics expanded the already existing boundaries of creativity in art assuring its use in the future.