Because early clarinets used felt pads to cover the tone holes, they leaked air. This required pad covered
holes to be kept to a minimal, proscribing the variety of notes the clarinet could play with good tone. In 1812, Iwan Müller, a Baltic German group born clarinetist and inventor, developed a new form of pad that was covered in leather-based or fish bladder. It was airtight and let makers increase the variety of pad covered holes. Müller designed
a new variety of clarinet with seven finger holes and thirteen keys. This allowed the instrument to play in any key with near equal ease.