Tuesday, October 16, 2007
The Medium Of The Moment
Deidre Stein Greben writes about advent of photography in the art world + the impact + the new collectors (private, trade, institutions) + the desirability factors + other viewpoints @ http://artnews.com/issues/article.asp?art_id=1259
The Geuda Story
Geuda is the milky corundum, formerly discarded as worthless by the Sinhalese cutting industry that constitutes the greatest reserve of high quality heat-treatable material available. Experts believe Sri Lanka, by common consenses, has the world’s largest deposits of this particular type of corundum rough.
The term geuda itself refers to a semi-transparent to semi-translucent corundum which appears silky or milky under reflected light (normal viewing conditions), but viewed under transmitted light (the light traveling through the stone before reaching the eye) gives a characteristic ‘tea’ color known in the trade as the ‘diesel’. Both these effects are due to the presence of impurities within the crystal, that under the correct heat treatment procedures it can (if the concentrations are correct) give rise to a strong blue coloration and an increase in transparency.
Milky Or Silky Effect
This is due to the presence of inclusions of rutile (TiO²). These may be in the form of long slender needles or as clouds of minute particles.
Diesel Or Tea Effect
Iron oxide impurities give rise to brownish patches or streaks that may or may not be randomly distributed through the crystal. Sometimes the oxide patches will be oriented parallel to the crystal faces.
Together these two sets of impurties have the potential to cause blue coloration if unlocked from the structure of the crystal and allowed to combine. These color causing agents (iron and titanium) may be activated by heating the corundum under certain conditions at around 1650ºC. If the most favorable ratio of iron/titanium is present a fine blue color of uniform distribution may be achieved, as will considerable improvements in transparency and luster. In general, the degree of milkiness and the intensity of the diesel effect are proportional to the color that results from heat treatment. Less diesel will result in a pale or lighter shade of blue, while intense diesel will give a dark blue color. If there is too much silk or milkiness, it is possible that some will remain after heating, which will influence the eventual transparency.
Local Classification Of Geuda
Over the years a considerable number of names, and a local classification have evolved. Here are a number of the most frequently used terms:
Diesel Geuda: Milky white intense brownish diesel.
Silky Geuda: Intense inclusions of rutile in the form of silk. May often display a strong diesel effect. Often further classified by its body color (yellow silky geuda)
Waxy Geuda: Material with waxy or dull appearance. May show a moderate diesel effect.
Milky Geuda: Dull white milky appearance with a diesel effect. The term blue geuda will refer to a blue milkiness with a diesel effect, while yellow geuda will indicate material with a yellowish milkiness, and so on.
Young Geuda: May be any body color, with a small amount of silk and/or diesel effect.
Thick Geuda: Opaque material with characteristic intense milkiness or diesel effect causing a dramatic reduction in transparency.
Dalan Geuda: The lowest grade of material made of mixed varieties (rejects) of geuda, usually with little silk or diesel effect. The lowest potential for successful treatment.
These coloquial names are based on the degree of concentration of the milkiness (observed under reflected light) and the intensity of the diesel effect (observed with transmitted light). The terms can be quite subjective, however, with different dealers categorizing the same materials under different names. For instance a milky geuda with a intense diesel effect may be described as diesel or milky.
The term geuda itself refers to a semi-transparent to semi-translucent corundum which appears silky or milky under reflected light (normal viewing conditions), but viewed under transmitted light (the light traveling through the stone before reaching the eye) gives a characteristic ‘tea’ color known in the trade as the ‘diesel’. Both these effects are due to the presence of impurities within the crystal, that under the correct heat treatment procedures it can (if the concentrations are correct) give rise to a strong blue coloration and an increase in transparency.
Milky Or Silky Effect
This is due to the presence of inclusions of rutile (TiO²). These may be in the form of long slender needles or as clouds of minute particles.
Diesel Or Tea Effect
Iron oxide impurities give rise to brownish patches or streaks that may or may not be randomly distributed through the crystal. Sometimes the oxide patches will be oriented parallel to the crystal faces.
Together these two sets of impurties have the potential to cause blue coloration if unlocked from the structure of the crystal and allowed to combine. These color causing agents (iron and titanium) may be activated by heating the corundum under certain conditions at around 1650ºC. If the most favorable ratio of iron/titanium is present a fine blue color of uniform distribution may be achieved, as will considerable improvements in transparency and luster. In general, the degree of milkiness and the intensity of the diesel effect are proportional to the color that results from heat treatment. Less diesel will result in a pale or lighter shade of blue, while intense diesel will give a dark blue color. If there is too much silk or milkiness, it is possible that some will remain after heating, which will influence the eventual transparency.
Local Classification Of Geuda
Over the years a considerable number of names, and a local classification have evolved. Here are a number of the most frequently used terms:
Diesel Geuda: Milky white intense brownish diesel.
Silky Geuda: Intense inclusions of rutile in the form of silk. May often display a strong diesel effect. Often further classified by its body color (yellow silky geuda)
Waxy Geuda: Material with waxy or dull appearance. May show a moderate diesel effect.
Milky Geuda: Dull white milky appearance with a diesel effect. The term blue geuda will refer to a blue milkiness with a diesel effect, while yellow geuda will indicate material with a yellowish milkiness, and so on.
Young Geuda: May be any body color, with a small amount of silk and/or diesel effect.
Thick Geuda: Opaque material with characteristic intense milkiness or diesel effect causing a dramatic reduction in transparency.
Dalan Geuda: The lowest grade of material made of mixed varieties (rejects) of geuda, usually with little silk or diesel effect. The lowest potential for successful treatment.
These coloquial names are based on the degree of concentration of the milkiness (observed under reflected light) and the intensity of the diesel effect (observed with transmitted light). The terms can be quite subjective, however, with different dealers categorizing the same materials under different names. For instance a milky geuda with a intense diesel effect may be described as diesel or milky.
Advice For The Young
(via designboom) Italian designer Guilio Iacchetti writes:
Be silent, and listen a lot
After that, then you can ask and talk.
I liked this one.
Be silent, and listen a lot
After that, then you can ask and talk.
I liked this one.
Heat From The Street
Energy: The Economist writes about new way (s) of collecting solar energy + innovative technique (s) used by Arian de Bondt, an engineer from Dutch building company called Ooms + other viewpoints @ http://www.economist.com/science/tq/displaystory.cfm?story_id=9933350
Kayne West
(via Rob Bates) I liked the Kayne West video on diamonds @ Diamonds from Sierra Leone + now has jewelry line.
De Beers Dandelion Diamond
(via Rob Bates) I liked the De Beers' Dandelion Diamond commercial (here) + the Spotrunner presentation + the DPS info @ dps.org
Demoralization, Resentment, Anxiety, Stress
Amei Wallach writes about the growth of museum (s) + the corporatization + the creation of the Association of Art Museum Curators (AAMC) for ethical/professional policies + other viewpoints @ http://artnews.com/issues/article.asp?art_id=1241
Tortoise Shell vs. Imitations
For thousands of years Tortoise shell has been associated with jewelry and personal items such as combs, eyeglass frames and art objects. They were popular with both the ancient Greeks and wealthy Romans. Many types of tortoise shell objects have been used for furniture inlays, eyeglass frames, decorative boxes, rings, bracelets, and earrings. In Japan, tortoise shell crafting or bekko, has been an important industry since at least the 17th century, centered in Nagasaki. Bekko objects such as hair ornaments are still being created today from stockpiled material. The source material comes from two species of sea turtles: the hawksbill and the rare green turtle. The shell tend to show attractive patterns from light to dark brown patches and other desirable shades. The popularity of tortoise shell from 18th through 20th century caused these animals almost to extinction leading to a near-worldwide ban in the 1970s + international trade in tortoise shell products.
Common imitations include plastic, phenol formaldehyde resin (bakelite), polyester resins (PET and polyurethane) among many others. Sometimes the identification could be a challenge for various reasons. For instance plastics and horn can imitate blond tortoise shell quite easily and the differences in luminescence may not be always diagnostic. Plastic (s) could be altered via change (s) in its chemical compositions, polymerization or the applications of dyes. Identifications may not be always that easy. Since tortoise shell and their imitations are fashioned into ornamental materials, standard tests beyond UV luminescence and hotpoint may not always be possible. It’s catch-22. According to experts, Tortoise shell and its imitations can be identified with standard (microscope, refractive index, specific gravity, UV fluorescence, etc) + analytical (photoluminescence spectroscopy, transmission infrared spectroscopy, specular reflectance infrared spectroscope, vis-nir spectroscope, raman spectroscopy), gemological tests.
Common imitations include plastic, phenol formaldehyde resin (bakelite), polyester resins (PET and polyurethane) among many others. Sometimes the identification could be a challenge for various reasons. For instance plastics and horn can imitate blond tortoise shell quite easily and the differences in luminescence may not be always diagnostic. Plastic (s) could be altered via change (s) in its chemical compositions, polymerization or the applications of dyes. Identifications may not be always that easy. Since tortoise shell and their imitations are fashioned into ornamental materials, standard tests beyond UV luminescence and hotpoint may not always be possible. It’s catch-22. According to experts, Tortoise shell and its imitations can be identified with standard (microscope, refractive index, specific gravity, UV fluorescence, etc) + analytical (photoluminescence spectroscopy, transmission infrared spectroscopy, specular reflectance infrared spectroscope, vis-nir spectroscope, raman spectroscopy), gemological tests.
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