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Flint Glass
Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00. Traditionally, flint glasses were lead glasses containing around 4–60% lead(II) oxide; however, the manufacture and disposal of these glasses were sources of pollution. In many modern flint glasses, lead oxides are replaced with other metal oxides such as titanium dioxide and zirconium dioxide without significantly altering the optical properties of the glass. Applications A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet lens because of their compensating optical properties, which reduces chromatic aberration (colour defects). History With respect to glass, the term ''flint'' derives from the flint nodules found in the ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crown Glass (optics)
Crown glass is a type of optical glass used in lenses and other optical components. It has relatively low refractive index (≈1.52) and low dispersion (with Abbe numbers between 50 and 85). Crown glass is produced from alkali-lime silicates containing approximately 10% potassium oxide and is one of the earliest low dispersion glasses. History The term originated from crown-glass windows, a method of window production that began in France during the Middle Ages. A molten blob of glass was attached to a pole and spun rapidly, flattening it out into a large disk from which windows were cut. The center, called the "crown" or "bullseye", was too thick for windows, but was often used to make lenses or deck prisms.''A Dictionary of the English Language - Volume 1, Part 1'' by Samuel Johnson, Robert Gordon Latham, Henry John Todd -- longmans, Green & Co. 1866 Page 314 Types The borosilicate glass Schott BK7 ( glass code 517642) is an extremely common crown glass, used in precisi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cup Plate
Cup plates are coasters that provide a place to rest a tea cup while leaving space for a light snack. Teacup plates originated in England in the early 1800s and went out of fashion in the second half of the 19th century (Barber puts the peak of popularity in the US at 1840s), with a brief reappearance in the first third of the 20th century as bridge sets. The cup plates were in common use in the United States during the first half of the 19th century, and were a precursor of the very specialized dishes of Victorian era: ice cream sets, berry sets, lemonade sets, etc. Use Shadel remarks that "it is difficult to pin down hefirst use" of the plates, and suggests that the ceramic plates arrived early in 1820s, with glass ones following in 1827, made by the New England Glass Company. Barber indicates the original use of the plates as a rest for the partially empty teacup that protected the tablecloth and the table surface (similar to the modern drink coaster), while the tea was c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromatic Aberration
In optics, chromatic aberration (CA), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the wavelength of light. The refractive index of most transparent materials decreases with increasing wavelength. Since the focal length of a lens depends on the refractive index, this variation in refractive index affects focusing. Since the focal length of the lens varies with the color of the light different colors of light are brought to focus at different distances from the lens or with different levels of magnification. Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image. Types There are two types of chromatic aberration: ''axial'' (''longitudinal''), and ''transverse'' (''lateral''). Axial aberration occurs when different wavelengt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lead Crystal
Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by mass) lead(II) oxide (PbO), while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO. Lead glass is often desirable for a variety of uses due to its clarity. In marketing terms it is often called crystal glass. The term ''lead crystal'' is, technically, not an accurate term to describe lead glass, because glass lacks a crystalline structure and is instead an amorphous solid. The use of the term remains popular for historical and commercial reasons, but is sometimes changed to simply ''crystal'' because of lead's reputation as a toxic substance. It is retained from the Venetian word to describe the rock crystal (quartz) imitated by Murano glassmakers. This naming convention has been maintained to the present day to describe dec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potash
Potash ( ) includes various mined and manufactured salts that contain potassium in water- soluble form.Potash , USGS 2008 Minerals Yearbook The name derives from ''pot ash'', plant ashes or soaked in water in a pot, the primary means of manufacturing potash before the Industrial Era. The word '''' is derived from ''potash''. Potash is produced worldwide in amounts exceeding 71.9 million |
George Ravenscroft
George Ravenscroft (1632 – 7 June 1683) was an English businessman in the import/export and glass making trades. He is primarily known for his work in developing clear lead crystal glass (also known as flint glass) in England. Personal life Little is known about Ravenscroft's personal life, character or appearance, though his father described him in his will as a responsible family man and an astute businessman. He was born in 1632, the second of five sons of Roman Catholic parents who hid their true faith and lived outwardly as Anglicans, and he was baptized in Alconbury Weston, Huntingdonshire, England, in April 1633. From 1643 to 1651 Ravenscroft attended the English College in Douai, France to train for the priesthood, but he dropped out before finishing his training and returned to London by 1666. After settling in London and establishing a successful import/export business that made him wealthy, Ravenscroft married Hellen Appleby, from Yorkshire, England, in 1670 or 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires. Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.''The Flints from Portsdown Hill'' Inside the nodule, flint is usually dark grey or black, green, white, or brown in colour, and has a glassy or waxy appearance. A thin, oxidised layer on the outside of the nodules is usually different in colour, typically white and rough in texture. The nodules can often be found along s and [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromatic Aberration
In optics, chromatic aberration (CA), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the wavelength of light. The refractive index of most transparent materials decreases with increasing wavelength. Since the focal length of a lens depends on the refractive index, this variation in refractive index affects focusing. Since the focal length of the lens varies with the color of the light different colors of light are brought to focus at different distances from the lens or with different levels of magnification. Chromatic aberration manifests itself as "fringes" of color along boundaries that separate dark and bright parts of the image. Types There are two types of chromatic aberration: ''axial'' (''longitudinal''), and ''transverse'' (''lateral''). Axial aberration occurs when different wavelengt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Properties
The optical properties of a material define how it interacts with light. The optical properties of matter are studied in optical physics (a subfield of optics) and applied in materials science. The optical properties of matter include: *Refractive index * Dispersion *Transmittance and Transmission coefficient *Absorption *Scattering *Turbidity *Reflectance and Reflectivity (reflection coefficient) *Albedo *Perceived color *Fluorescence *Phosphorescence *Photoluminescence *Optical bistability *Dichroism *Birefringence *Optical activity *Photosensitivity A basic distinction is between isotropic materials, which exhibit the same properties regardless of the direction of the light, and anisotropic ones, which exhibit different properties when light passes through them in different directions. The optical properties of matter can lead to a variety of interesting optical phenomena. Properties of specific materials *Optical properties of water and ice *Optical properties of carbon nano ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Achromatic Doublet
An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus on the same plane. Wavelengths in between these two then have better focus error than could be obtained with a simple lens. The most common type of achromat is the achromatic doublet, which is composed of two individual lenses made from glasses with different amounts of dispersion. Typically, one element is a negative (concave) element made out of flint glass such as F2, which has relatively high dispersion, and the other is a positive (convex) element made of crown glass such as BK7, which has lower dispersion. The lens elements are mounted next to each other, often cemented together, and shaped so that the chromatic aberration of one is counterbalanced by that of the other. In the most common type (shown), the positive power of the crown lens element is not quite e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices such as telescopes, binoculars, and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word ''lens'' comes from , the Latin name of the lentil (a seed of a lentil pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
