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OPAL EDUCATION Contents:
This is only the beginning of our educational material on OPAL. Please check back from time to time as this area (as well as our product area) will continue to expand. We will continue to add more photos, providing better visual representation of this educational material. This is a working document so expect regular updates as we are able!
HOW TO SPOT A FAKE! The single most significant problem in the gemstone industry today is treated, simulated or synthetic gemstones. Specifically, stones being sold without disclosure as to their synthetic or simulated composition. Unfortunately, this is also true in the OPAL industry. There are hundreds of unscrupulous persons out there that want to take a pile of your money and give you a fake in exchange. (Please note that NO synthetic opal is found on the House of Opal website, opalhouse.com. We made the decision not to sell that type of material here to avoid ANY confusion. ALL the opal on this site is Australian opal, Mexican opal or as otherwise specified. Australia provides over 90% of the natural/authentic opal for the world.) For example, if you look at many of the sterling silver and even 14K & 18K gold rings, pendants and earrings on eBay.com & other sites on the Internet, you will see many, many of them match "perfectly". Although Kabana does use some natural opal, any of the "Kabana" styled "clone" pieces are made from synthetic or fake opal. They have the same pattern (actually there are two patterns) and are divided into shades of white/clear, blue (called "black opal"), green (also called "black opal") and even red. To find two opals that "match" (they won't be identical even if they came from the same piece of rough) is truly a RARE thing, although it does happen occasionally. What would a pair of these matching stones cost? Well, if they are black opals - say a pair of 7x5mm ovals, they could cost anywhere from $200 per carat to $5000 per carat. Ok, so how much is that? They would weigh approximately 0.5 carats each, for an approximate of 1 carat total, meaning $200~$5000.00. That said, if you find a seller offering a MATCHED PAIR of Black Opal stones for say, under a hundred bucks, you can pretty much count of them being fake. What do I mean by fake? These stones, essentially made of glass, can be cast directly into silver and gold jewelry, making jewelry production by machine "super cheap". It's a great idea as a manufacturer and cuts finish time to almost nothing by comparison. (Hand cutting and setting individual stones for inlay is quite time consuming and requires great care & skill in order to be done correctly.) BTW, touch an opal with over 200 degrees of temperature and you will likely destroy it - we'll have more on that later on our "Opal Care" page. If you are looking for a pretty piece of jewelry, no problem - make your selection from the myriad of these inexpensive products and enjoy. Just don't say it's an opal... And don't let the seller tell you it is, either. You WILL NOT find synthetic opal, simulants, fakes, etc. for sale on THIS SITE. PERIOD. If you want to have a real opal, something unique -- the ONLY ONE in the WORLD like it... then you should read on a bit more. We inventory ONLY real/authentic/natural opal. Natural opal is divided into an array of types of opal and a few types of physical construction for "assembled" stones (our assembled stones are made from natural opals). More on that in a bit. TYPES OF OPAL: Black Opal, White Opal, Milky Opal, Crystal Opal, Seam Opal, Jelly Opal, Contraluz Opal, Potch, Boulder Opal, Koroit, Yowah, Mintabie, Lightning Ridge, Solid Opal, Opal Doublets, Opal Triplets, and the list goes on... Whew! With a list like that being only the beginning, how does one know what to get? Well, lets start with mining. In the rough, opal may be found in thin fissures and cracks in a "parent" rock. While found in fissures, beds and cracks, there are a variety of replaced organic materials such as opalized wood, shells and even compledinosaurs! Most often in Queensland, Australia opal is found in ironstone but it can also be found in sandstone. In sandstone it may be found in conjunction with the sandstone, as if it is "soaked" into the sandstone. Ocassionally, it is found in thicker deposits called seams or bars. HOW TO JUDGE AN OPAL: Determination of the type and subsequent valuation of an opal relies on: Body Color, Brightness, Fire Color, Fire Pattern, Carat Weight, Shape, Cut & Inclusions. The locale that the rough material was mined may also add, or detract, from the value.
BODY COLOR: Body Color refers to the base color or background color of the stone. Black is a body color, as is White, Milky, Jelly and Crystal (or clear) opal. If you were looking at a group of stones and all were the same in every respect but body color, the ones tht would "jump out" at you would be first, the BLACK, then the CRYSTAL. Crystal opal is completely transparent - you can read text through it - and has nothing to diffuse the color of the stone. The most spectacular opals are BLACK. Top-quality Black opals are a layer of bright Crystal opal on a black body color (black common opal potch). The black ensures that no light escapes the stone except that portion returned back to you to see. In other words, ambient light really doesn't affect it. If there is enough light to see the stone, it is going to be beautiful. The more light the more beautiful. The "black" is actually "common" opal Potch. Potch is still opal but does not have the silica spheres aligned in a manner that light is returned back to you. Instead, potch is comprised of mismatched sizes of silica spheres in random patterns. Main colors are black, grey, white & brown. Transparent crystal without fire is often faceted, especially when it is orange to red in body color and from Mexico and is referred to as "Fire Opal". Shown below are stones with body color of crystal (over a partly black background to show transparency), semi-crystal, milky, light gray, dark gray and black.
Stones body color is further refined by an "N-scale" (AGIA Body Tone Scale) going from N1~N4 (BLACK Opal) to N5~N6 (DARK Opal) to N7~N9 (LIGHT Opal). BRIGHTNESS: Brightness relates to the amont of light refracted or reflected back to you from the stone by a light source. The best light source is unquestionably the Sun. When possible, we take photos in natural sunlight at around 11AM to 2PM. Why so pickey? This time of day provides the best light temperature (@5500~6500 Kelvin) & the best color reproduction. It is, in fact, the only way to properly judge an opal. A brightness scale was, if not pioneered by, at least published and more widely distributed by Paul Downing. The "Brightness Scale" is made up of 5 levels of brightness. The levels could be best described in words as "Oh, that's an opal?" to "Holy cow! It's blinding me!!" Seriously, a level 5 stone viewed in sunlight can actually damage your eyes if you look at it too long! The concept of the scale is based upon 3 stones of "known" value. If you have a level "2" brightness stone, a level "3" and a level "4"; you then know which of the five levels the stone in question is. How? If it is less bright than the level 2 or more bright than the level 4, or between two of the other levels, it makes it easy to decide! Shown below are some examples. Don't use this as a scale because depending upon the brightness of the monitor, the color settings, etc. it will look different. Below are stones in levels 2, 3 & 4 simply as a guideline/example.
FIRE COLOR: Fire color may be seen in ANY color of the rainbow. Yes, really. Although the bulk of what people consider to be "opal" is white or milky base material with multicolour pinfire, that is only a PORTION of what is available in opal. Below are some examples of different fire colors. FIRE PATTERN: Fire Pattern is a HUGE area that has filled many books. Here we will review some of the main patterns. Note: a single opal may exhibit one, several, or many different patters. Harlequin: Harlequin pattern is characterized by large blocks of color. The most prized harlequin has the appearance of a "court clown's" braided silk, with a cross-hatch woven appearance that may even appear to be tucked at the edge of each color! Subcategories: Floral, Flagstone, Square, Hexagonal & Cloverleaf. Chinese Writing: Chinese Writing pattern opals have differing colors of "slashes" that have an appearance similar to Chinese text or calligraphy. Mackerel Sky: A Mackerel Sky pattern has the appearance of, well, the side of a mackerel! Moss: Moss pattern has the appearance of a very irregular "mossy" pattern. Rolling Flash: Rolling Flash is a pattern that "rolls" across the stone as it is rotated. this is different thank a "directional" stone, which may only show color from a single angle. CARAT WEIGHT: Carat* weight is fairly straightforward.
Rough opal is sold by carat, gram or TROY ounce in the trade. There are 12 TROY ounces to a TROY pound. A TROY ounce is 1.0972 AVOIR ounces. Depending upon the rough and the person cutting it, an ounce of opal my yield as much as 60% of finished weight in gems (rare) or as little as 1%. Normally yield is between 50% and 25%. Shape of the rough, amount of color, health (whether there are a lot of cracks) and inclusions all are factors. * Please note that CARAT differs from KARAT. KARAT is used as a purity measurement of 1/24th of a whole for gold. eg: 18K gold is 18/24ths pure gold or 75% gold and 25% alloy. 14KY gold is 14/24ths or 58.3% pure gold. SHAPE: The most common shape for opal is the oval. Opals are also cut into round, pear, marquise/navette, triangle, square, rectangle, cushion, variants of the preceeding or freeform shapes. Opal is sometimes cut and inlaid into other opal, other stones or metal. CUT: Quality of the Cut is very important. The direction or facing up if the stone that is done when in the opal is in rough form has a direct impact upon the way a piece looks when finished. Often a piece of opal rough will be brighter from one side than the other. Sometimes a color bar looks great from the edge but poor (by comparison) on the "front". These are all considerations when cutting opal. Unfortunately, one frequently does not know until one starts cutting. One of the best ways to minimize waste is to buy a large parcel, then experiment with some of the smaller pieces. If the material all came from the same find or seam, it may have similar properties throughout the material. Once the stone is "faced up" properly, meaning that the brightest color is toward the face of the stone, then shaping can begin. There are two types of shaping to discuss here. First is the outside/perimeter shape of the stone as discussed above. Then there is the cross-sectional shape of the stone. Make a stone too flat and thin and it may break easy. Make it too thick and it may be almost impossible to set properly. somewhere in the middle is best. Proper proportions come through experience. Often black opal is cut with a "fat belly" - meaning that a lot of extra material is left on the bottom that may (or may not) be opal potch. This is done to increase carat weight and increases the value of the stone (because it is sold by the carat). An arguement can certainly be made that the rounded belly positively impacts the strength of the finished stone. When cutting calibrated stones such as ovals, we usually cut our stones in a more "commercial" cut so that they will fit better in standard industry settings.
COLOR SATURATION: Color Saturation is a relatively new term. It is the amount of color that one sees in comparison to the background/body or inclusions. The higher the saturation, the more impressive the stone, and the higher the price.
CONSTRUCTED STONES: Constructed or assembled stones are generally slices of gem material that are attached to non-gem material with the use of industrial adhesives such as epoxy. These constructed or assembled stones are usually made with a thin slice of gem opal, coupled with other transparent or opaque materials. In opaque materials, a layer of black lab glass, obsidian, black jade, basalt, black opal potch (non-precious opaque opal, black in color), or in some cases even plastic has been used. Occasionally a layer of black paint may be used as a coloring, or a manufacturer may add opaque black agents to the epoxy mix to create a black layer behind the slice of gem opal. Why the fuss? Why bother to go through so much work? The key intent is usually to simulate or imitate the appearance of high-quality black opal. This effort is very worthwhile. The end result may be from thin layers of opal that, while beautiful, could not have been used any other way, but are able to be used in this manufacturing process. Most often though, very high quality opal is sliced into thin sections by a saw (photos coming). These slices may be so thin as to get 100 slices per inch of opal. You may be thinking... "What a ripoff!?!"... Not so. The quality of the opal used has a direct result upon the final appearance of the material. It is really quite simple - use $1 per gram material to produce doublets or triplets and you get cheap, ugly finished pieces. Use $100 per carat material and you may get some of the most beautiful and durable pieces possible - although that is not always the case... Cutting gem opal into thin slices has its own challenges... Opal has no crystalline structure. Therefore, unlike quartz, diamond and many other precious stones, it has inherent weaknesses. Any sort of interruption - power outage, equipment stall, failure of a part... can cause the complete and utter destruction (think crushed glass...) of thousands of dollars of opal rough. In less time than it takes to say... "OH, NO!!" Even in Australian dollars, that is a lot of money... More information will be added later, along with photos of the process, but here are the main points you need to know:
You are probably getting the picture... This is no easy task.
DOUBLETS: Doublets are constructed of two layers. Most frequently, a layer of gem opal and a layer of another material such as opal potch or ironstone as a backing material. Doublets may be constructed of a layer of gem opal and a layer of quartz, spinel, glass or other transparent material on the top; or may be made from two layers of gem opal - such as for a two-sided stone for a pendant. All are doublets. Doublet refers only to construction using two separate layers. Below are doublets of various costruction: Thin Gem or Noble Opal, backed with ironstone. Thick Gem Opal backed with lower-quality gem opal, black-colored epoxy between layers. Crystal Clamshell, backed with ironstone. Thick Gem Opal backed with natural black non-precious (potch or common) opal.
The most commonly available form of doublets are thin slices of precious or gem opal are attached to a backing. They may be sold as boulder opals or even BLACK opals by unscrupulous sellers. Doublets require extra care when setting and are easy to chip because the thin top layer of opal material may fracture easily. It is very difficult to set an opal doublet in a standard prong-type setting without damaging it. It is often more succeptable to damage while wearing because of the thin, exposed layer of opal. If you cannot set them in prong settings, what good are they? Doublets look beautiful in bezel settings and are very durable if resonable care is taken. (Note: Bezel settings surround the entire edge of the stone with a solid, very thin layer of gold or silver.) They have the appearance of a solid stone, yet are very inexpensive. Doublets will generally sell for between one-tweantyth to one-one hundredth of what a similar solid stone would sell for -- a BIG difference in price. To conclude, opal doublets, properly set in a bezel, offer beautiful jewelry with the appearance of black opal that may be hundreds or even thousands of dollars per carat quality at "bargain-basement" prices! A very economical alternative! TRIPLETS: A triplet is constructed of three layers. These layers may include one or more layers of gem opal. Most frequently, opal triplets are constructed of a backing material such as black, gray or white opal potch, a thin slice of gem opal material and a top layer of clear material such as spinel, quartz or glass. Another form of triplet may be constructed of two layers of opal separated by black opal potch. More to come...
About different types of opal, opal fields, etc.: Black Opal is found throughout the world but the main supply is generally agreed to be the Lightning Ridge fields in Australia. There is also material found in the Mintabie field that is white to crystal material on black potch. Black opal is the most rare type of opal and typically sells for more per carat than diamonds! (to deBeers dismay, I'm sure...)
More to come...
Contributions: This information was written by my own hand, however, I have to give credit to the many great authors (Paul Downing and Barrie O'Leary for example) that contributed through the years to my education as well as personal friends in the opal industry that have taken time to help me. I have read hundreds (thousands?) of articles and trade briefs on opal and the gemstone industry as well, and it would be impossible for me to list them all here. Also, I am not above being corrected... If you feel I have made an error somewhere, please contact me so we can get it (or you) corrected! : ) This information (C) (R)2008 House of Opal & opalhouse.com. |
Copyright 1996~2008 House of Opal & http://www.opalhouse.com/ - All rights reserved.