![]() In an interesting way, fire obsidian is one of the peak challenges of the lapidary arts. It’s usually sold per carat, as opposed to every other variety which is sold by the pound or piece depending on how much work has been put into the rough.įire obsidian is only found in a few places and if there’s anywhere else… people are staying tight-lipped about it. ![]() When it’s cut properly, fire obsidian will show an incredible array of bright colors when viewed from the proper angle.įire obsidian’s effect is created through thin-film interference, much like rainbow obsidian, but the material here is ultra-thin layers of magnetite instead of the hedenbergite that causes the colors in rainbow obsidian.įire obsidian is extremely expensive compared to most varieties. It’s the most expensive and rare type of obsidian and requires a ton of experience to cut properly to view the visible effect. Sheen Obsidianįire Obsidian (credit: Jessa and Mark Anderson/ Flickr)įire obsidian is… something else. ![]() There are great places to find it in each state along the Western Coast of the USA, and some great examples also come from Mexico. Rainbow Obsidian is the second most expensive type of obsidian most of the time, but it’s very affordable compared to Fire Obsidian. This effect is caused by thin-film interference, think of it as a solid oil slick effect. This mineral is oriented in the rainbow obsidian and causes light entering the stone to act differently. The cause of this coloration? Nano-rods of hedenbergite. Rainbow obsidian can range from full-facing, incredible pastel colors to a barely visible sheen form an oblique angle. Some of the most striking examples are found in the aptly named Rainbow Mine in the Warner Mounts area. ![]() Rainbow obsidian is a prized material, varying greatly in colors. Before the discovery of fire obsidian, which has a much more intense effect, it was among the most expensive types. It ensures that the glass surfaces do not crack and that the glass does not come into mechanical contact with things during use that could scratch the surface.Rainbow obsidian is a variety that exhibits a rainbow pattern in concentric rings when the light hits the surface just right. The strength of the glass can be improved by up to a factor of 10 with this method. The cracks are therefore "kept closed by the constant residual stress. Thermal or chemical treatment of the glass so that the outer surfaces are under relatively high compressive stress, while the middle area between the surfaces is under tensile stress. There are two methods to reduce/eliminate this problem: Glass has no mechanisms to reduce the resulting high local stresses and is therefore subject to rapid brittle fracture. The reason for the weak tensile strength of glass is that it is usually covered by microscopic cracks that create local stress concentrations. Therefore, most of the glass breakage is due to the failure of tensile strength. However, glass can withstand extremely high compressive stresses. The practical tensile strength of the glass is about 27MPa to 62MPa. A special surface treatment can minimize the effects of surface defects. It is only weakened by surface defects, which give everyday glass its fragile reputation. That is why this glass is widely used in chemical plants and for laboratory equipment. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkalis cause significant corrosion of the glass. It also has moderate resistance to alkalis. These items are generally used at temperatures up to 250oC.īorosilicate glass has a very high resistance to the attack of water, acids, salt solutions, halogens and organic solvents. ![]() In the household, borosilicate glass is known in the form of stoveware and other heat-resistant household items such as Pyrex. This glass is used in the manufacture of glass fibers for use in plastic and textile reinforcements - see below Due to its thermal and optical properties, it is widely used for high-intensity lighting applications. It is therefore widely used in photochemistry. The maximum recommended working temperature (short-term) for borosilicate glass is 500oCīorosilicate glass has good optical properties with the ability to transmit light through the visible region of the spectrum and in the near ultraviolet range. Borosilicate glass has exceptional thermal shock resistance, as it has a low coefficient of expansion (3.3 x 10 -6 K-1) and a high softening point. Borosilicate glass has a relatively low alkali content and, as a result, high resistance to the attack of water. Glassware is often used in laboratories where repeated contact with water vapor at high temperatures can leach alkali ions. Borosilicate glass is made from 70% - 80% silica (SiO2) and 7% - 13% boron oxide (B2O3) with small amounts of the alkali sodium oxide (soda) (Na2O) and aluminum oxide (AI2O3). ![]()
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