The speculum metal mirror from William Herschel's 1.2-meter (49.5-inch) diameter "40-foot telescope" at the Science Museum in London[1]Modern replica of Herschel's 6.2"-aperture Newtonian telescope which had a speculum metal main mirror
Speculum metal is a mixture of around two-thirds copper and one-third tin, making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to optical devices until it was replaced by more modern materials such as metal-coated glass mirrors.
Speculum metal mixtures usually contain two parts copper to one part tin along with a small amount of arsenic, although there are other mixtures containing silver, lead, or zinc. This is about twice the proportion of tin to copper typically used in bronze alloys. Archaeologists and others prefer to call it "high-tin bronze",[2] although this broad term is also used for other alloys such as bell metal, which is typically around 20% tin.
Large speculum metal mirrors are hard to manufacture, and the alloy is prone to tarnish, requiring frequent re-polishing. However, it was the only practical choice for large mirrors in high-precision optical equipment between the mid-17th and mid-19th centuries, before the invention of glass silvering.
Speculum metal was noted for its use in the metal mirrors of reflecting telescopes, and famous examples of its use were Newton's telescope, the Leviathan of Parsonstown, and William Herschel's telescope used to discover the planet Uranus. A major difficulty with its use in telescopes is that the mirrors could not reflect as much light as modern mirrors and would tarnish rapidly.
^"Original mirror for William Herschel's forty-foot telescope, 1785". Science Museum. Archived from the original on 2009-09-02. Retrieved 2008-11-23.
Speculummetal is a mixture of around two-thirds copper and one-third tin, making a white brittle alloy that can be polished to make a highly reflective...
coloured Speculum literature, a medieval genre Speculummetal, an alloy containing copper and tin used for making all-metal mirrors "Speculum", a song...
During the period 1850–1900, reflectors suffered from problems with speculummetal mirrors, and a considerable number of "Great Refractors" were built...
time of Newton to the 1800s, the mirror itself was made of metal – usually speculummetal. This type included Newton's first designs and the largest telescope...
layer on the surface of the metal. Bell metal Phosphor bronze Nickel bronzes, e.g. nickel silver and cupronickel Speculummetal UNS C69100 Copper is often...
exact metals used in the alloy are maintained as family secrets; metallurgists suggest that the alloy is a mix of copper and tin, so a type of speculum metal...
Isaac Newton built his first reflecting telescope. He chose an alloy (speculummetal) of tin and copper as the most suitable material for his objective mirror...
telescopes that succeeded it because of the poor performance of its speculummetal mirror. Chronological list of optical telescopes by historical significance...
remained common in many parts of the world until the 19th century. Speculummetal is a very hard high-tin bronze-type alloy, with about 30% tin rather...
non-disposable Kelly's rectal speculum, named after the American gynecologist Howard Atwood Kelly, is the most commonly used speculum for proctoscopy. Some proctoscopes...
parts: the Speculum Naturale, Speculum Doctrinale and Speculum Historiale. However, all the printed editions include a fourth part, the Speculum Morale,...
telescopes. He would spend up to 16 hours a day grinding and polishing the speculummetal primary mirrors. He relied on the assistance of other family members...
and India. Mirrors of speculummetal or any precious metal were hard to produce and were only owned by the wealthy. Common metal mirrors tarnished and...
ground his own mirrors out of a custom composition of highly reflective speculummetal, using Newton's rings to judge the quality of the optics for his telescopes...
problems seen in refractors, were hampered by the use of fast tarnishing speculummetal mirrors employed during the 18th and early 19th century—a problem alleviated...
is a spherical or parabolic shaped disks of polished reflective metal (speculummetal up to the mid 19th century), or in later telescopes, glass or other...
apertures than metal, and later glass, mirror telescopes. The technology for silver-coating glass mirrors, more reflective than speculummetal and not subject...
first optical-quality first surface glass mirrors, replacing the use of speculummetal mirrors in reflecting telescopes.[dead link] These techniques soon became...
died in 1897. Glass lens telescopes had a good reputation compared to speculummetal and silver on glass mirror telescopes, which had not quite proven themselves...
many advantages including a far better site, a glass mirror instead of speculummetal, and a precision mount which could accurately track any direction in...
romanized, include: "moon-mirror" "Yin mirror" "metalspeculum for gathering water from the moon" "square speculum" "square receptacle" Metaphorically using...
to their difficulty of construction and the poor performance of the speculummetal mirrors used it took over 100 years for reflectors to become popular...
techniques of casting, grinding and polishing large telescope mirrors from speculummetal, and constructed steam-powered grinding machines for parabolic mirrors...
Gregorian telescopes with parabolic mirrors made from the highly reflective speculummetal. The Gregorian telescope consists of two concave mirrors: the primary...
Global Information
