 The next major development in the history of clarinet was the invention of the modern pad. Because early clarinets used felt pads to cover the tone holes, they leaked air. This required pad-covered holes to be kept to a minimum, restricting the number of notes the clarinet could play with good tone. In 1812, Iwan Müller, a Baltic German community-born clarinetist and inventor, developed a new type of pad that was covered in leather or fish bladder. It was airtight and let makers increase the number of pad-covered holes. Müller designed a new type of clarinet with seven finger holes and thirteen keys. This allowed the instrument to play in any key with near-equal ease. Over the course of the 19th-century makers made many enhancements to Mueller's clarinet, such as the Albert system and the Baermann system, all keeping the same basic design. Modern instruments may also have cork or synthetic pads.
