From the time of Newton to the 1800s, the mirror itself was made of metal usually speculum metal. This type included Newton's first designs and even the largest telescopes of the 19th century, the Leviathan of Parsonstown with a 1.8 meter wide metal mirror. In the 19th century a new method using a block of glass coated with very thin layer of silver began to become more popular by the turn of the century. A major turning point in reflecting telescopes was the Paris Observatory 1.2 m of 1878, A.A. Common telescopes which led to the Crossley and Harvard reflecting telescopes, which helped establish a better reputation for reflecting telescopes as the metal mirror designs were noted for their drawbacks. Chiefly the metal mirrors only reflected about 2/3 of the light and the metal would tarnish. After multiple polishings and tarnishings the mirror could lose its precise figuring needed.