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Dichroic glass is glass containing multiple micro-layers of metal oxides which give the glass dichroic optical properties. The invention of dichroic glass is often erroneously attributed to NASA and its contractors, who developed it for use in dichroic filter. Dichroic glass dates back to at least the 4th century AD as seen in the Lycurgus cup.
Multiple ultra-thin layers of different metals (gold, silver), metal oxides (titanium, chromium, aluminium, zirconium, magnesium) and silica are vaporised by an electron beam in a vacuum chamber. The vapour then condenses on the surface of the glass in the form of a crystal structure. This is sometimes followed by a protective layer of quartz crystal. The finished glass can have as many as 30 to 50 layers of these materials yet the thickness of the total coating is approximately 30 to 35 millionths of an inch (about 760 to 890 nm). The coating that is created is very similar to a gemstone and, by careful control of thickness, different colours are obtained.
The history of the emerald is fascinating.. The name emerald is a derivative of an ancient Persian word, coming to us through the corruption of the Latin Smaragdus which really just means 'green gemstone'.
The first emerald mines recorded in history are the famous Cleopatra mines rediscovered in 1818 in Northern Egypt. Cleopatra adored jewellery and she loved the green gem stone above all others and once gave an emerald with her portrait engraved on it to at least one favoured ambassador. These ancient mines were exhausted long ago.
The emerald mines in Colombia have a history somewhat similar to those in Egypt. When the Spaniards conquered the Incas, they saw emeralds in their possession, but even under torture, these never revealed their source. Years later, one mine in the Chivor area in Colombia was discovered quite by accident
Pliny wrote, “nothing is more intense than the green of emerald” and “sight is refreshed and restored by gazing upon this stone”. Following his advise, Roman emperor Nero wore emerald sunglasses to watch the gladiators.
The Moguls of India loved emeralds so much that they inscribed them with sacred texts and wore them as talismans. This led to the flourishing Jaipur cutting industry.
Emerald is said to give a supernatural ability to foretell future events.
A surprising variety of virtues have been ascribed to emerald. Among these, emerald was thought to improve its owner’s memory and eloquence, and was also said to quicken intelligence. In a particular instance of emerald’s use, as a measure against ills, women wearing the stone were believed to be immune from epilepsy.
Fissures and fractures that are characteristic of emerald are traditionally filled with oil to minimize their visual impact. Cleaning emerald with an ultrasonic cleaner can remove or damage the oil, thus making the fissures more visible. This is the same for most detergents as well so if you have an emerald ring remove or cover before washing.
Emerald is the birthstone for May.
In the early 1990s a new type of opal surfaced in Ethiopia which was called Chocolate opal because of the chocolate colour inside the nodule. These opals are found in a round nodular form with in a 3 meter thick layer of welded volcanic ash. Only about 1% of these nodules contain colour. The colours are very striking with red being common and blue quite rare which is the opposite to Australian opals. It has some magnificent patterns and brilliant colours and is called Ethiopian fire opal.
Later opal was found in Gondar which was at first called desert opal but it is from a plateau in the highlands. The main field which is creating a lot of excitement now is from a field called Welo.
This is found in a plateau 2500 to 3299 meters. Only the locals are allowed to mine this field and the government has even supplied basic tools. They work the horizontal level of these steep mountains and unfortunately there have been fatalities due to the rock top collapsing. This field produces a variety of crystals, brown base and even black material. A very small percentage is called gum opal as if you wet your hand the opal sticks to it like gum!
Opals from this field are known as Ethiopian opal from wello.
A large majority of this material is hydrophane as if it is soaked in water the base colour can become clear increasing the play of colour or it can sometimes vanish. When dry this material is very bright. If it gets wet it may take a few weeks to dry out but don’t hurry the process. This is why some cutters cut it dry to prevent this.
Good Ethiopian opals have diverse play of colours from Neon reds, oranges, green, blue, white, yellow, brown and contra luz fire. Ethiopian fire opals are popular as they have striking pattern formations which make each opal so unique
Ethiopian Opals, from North Africa, have only begun to be mined recently. However, anthropologists report that around 4,000 years BC, early man used opals to make tools, which means that Africa mined opals before Australia.