Black Opal Brightness and Body Tone Guide
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black opal brightness and body tone guideThe Opal Body Tone Guide was designed and created by the Opal Association of Australia and acts as a guide for Black Opal and Boulder Opals. The Opal industry has recently also been using this guide for many Opal types including Ethiopian Opals.

Body Tone N1 - N4 - Is for black tone body types.

Body Tone N5 - N7 - Is for light coloured Opals mined also at Lightning Ridge but these lower body tone grades can and have been used on Coober Pedy Opals and Ethiopian Opals.

Opal Brightness Guide

The Opal Brightness Guide assists in assigning a value to how bright an Opal is to the naked eye.

Brightest 1 to & Dullest 7 - Can be used on any Opal with 3.5 as average brightness for many opals considered commercial grade.

Brightness lower than a 3 - Is considered a B grade Opal or low Commercial grade.

How is Opal Color Produced?

Opal formation

The local name given potch, such as desert sandstone, is dependent upon the area in which they occur, but they all belong to the same families of felspathic sandstone, claystone, siltstone and mudstone, which are said to have been deposited over large areas buy streams and lakes.

We call any material that opal colour has formed on as Potch. Except for volcanic opal, which usually occurs in Tertiary rocks, all the types of opal we have come to know so well are found in these strata. Although the opal is found in the Cretaceous sediments, it is a matter of conjecture as to it’s deposition over millions of years during the Tertiary period. The general teaching is that certain minerals were broken down in the country rock to produce silica at 120 parts per million, and trace elements which were deposited in cavities left by bones, shells and other dissoluble material. These, as well as faults and fractures in the ground, provided pathways for the underground waters to carry the silica down at the end of the weathering period.

Although this is the entrenched theory, with “slight variations” depending on your source of information, it is fraught with problems which have been deleted from the model to give it credence. There is little doubt that all opal was not deposited in exactly the same manner. So far I have discovered four different ways in which it has been deposited; there may be more. They all have a common denominator in the equation, ionic-exchange. The fact is that opalization is extremely regional and that large beds of impervious barriers are only secondary to opal formation.

If the only requisite for opalization under the above model were suitable impervious traps, then there would be massive beds of opal over vast areas. However, as every opal miner knows, this is not the case and all opal is unpredictable and patchy in the extreme.

Australian Opal is rarely faceted, nearly always domed. A domed stone is stronger and less prone to chipping. However Opal without a play of color (such as cherry red or amber Opal from Mexico) is often faceted and can look a lot like ruby. Opals are a carver’s delight. The stone is not too hard to work with and will not wear out your diamond tools as much as such stones as Chrysoprase and Agate.

Opal Size

Popular sizes are listed below.

Round: 5 mm and 6 mm

Oval: 6 x 4, 7 x 5, 8 x 6, 9 x 7, 10 x 8, 12 x 10, 14 x 10, 16 x 12, 18 x 13, 20 x 15, 25 x 18, 30 x 22, 40 x 30.

Opal Settings

Jewellery castings for opals can range from very simple designs to very ornate designs with accent diamonds.

There are some interesting myths associated with Opal settings. Some folks believe that Opal Doublets and Triplets are always put into fully backed settings to hide the potch backing. Others believe that full backings are used to protect the stone. Neither myth is true. A jeweler could just as easily “hide” a doublet in an open backed setting, as the join line between the stone and the potch backing would be covered by the side of the setting, making it difficult to see whether the back of the stone was a different stone or simply the less brilliant side of the same stone.

How Opal is Graded and Sold

Rough Opal parcels are sorted into three grades: tops, middle, and low. Each tops parcel has a King stone, which is the best stone in the parcel. Some parcels have several King stones. Color is the primary criteria for grading, but the graders also take into consideration the number of imperfections and faults, and whether a stone is the right shape to be cut into an oval or one of the other popular shapes. You can buy rough opal in several different conditions.

Mine Run

Direct from the mine. The stones have not been cut or ground down. This means that there is more guesswork in the cutting. Purchasing mine run opal can be risky if you are not very experienced.

Off Cuts

The miner has removed whatever black opal rough ,he has a market for and sells you what’s left. With off cuts, you can usually tell what you are going to be able to cut. You must still watch for cracks in the opal because once a crack becomes obvious, a stone can lose half its value.


This can often be the best way of buying black opal rough if you are not very experienced. The miner has cut and ground the stones into basic shapes, after having removed most of the rubbish. What you have left is the stone nearly ready for the dopping and polishing process. You have the satisfaction of cutting your own stones without the high risk of buying mine run rough.

Opal is officially sold in troy oz. There are approximately 30 grams to a troy oz and approximately 30-oz to a kilo.

Hints and Tips

Here’s an eclectic assortment of hints and tips you may find helpful when buying or working with opal.

1. Not all Opal is valuable. Potch, is sometimes called “common opal” does not reflect colors. Potch does have its use, however, as a backing for doublets and triplets. When there is color mixed with potch it’s called “potch and color.”

opal potch

2. Some classes of rough Opal are unsuitable for making gemstones. Some are very porous. Others have a chalky appearance. Still others can lose their color in a short period of time. And yes, it is common for certain types of opals to shatter in a dry atmosphere when the water from the gel evaporates. The best protection for buyers is to purchase opal from a knowledgeable and reputable dealer who accurately details exactly what you are purchasing and is willing to guarantee the stones. Note: If you buy rough opal, there is no guarantee that it will not crack. This is the calculated risk you take and is part of the “excitement” of opal cutting. opal potch

3. When examining opal jewellery, look at the stone from the side to determine whether it’s a triplet. Solid and doublet opal domes are simply the opals formed into a curved dome shape. Triplets have clear crystal domes to protect the flat opal surface.

4. It is very difficult to tell whether a stone is a doublet or a solid if it is in a setting. It helps if the back of the setting is open, but it is still no real indication because the back of a doublet and a solid looks very similar, although a doublet is usually perfectly black on the back whereas a solid black opal usually has some imperfections. So if the back of a stone looks too perfect, you have to be a little suspicious. For this reason it’s best to buy opal from reputable dealers who know what they are doing because, unfortunately, many jewelers also are not experienced in opal.

5. When buying opal over the net, ask the seller to give you a summary of how close the graphic sample is to the real thing. Opal is very difficult to photograph and the appearance on the computer screen may give it a different look. Particularly is this the case in regards to size. Graphics come out in all different sizes, usually a lot larger than actual…so make sure you get your ruler out and actually draw the size on a piece of paper so that you will know in your own mind’s eye the actual size of the stone.

6. The same thing applies to the color of the stone. Make sure you get the supplier to give a commentary on the color so that you will know pretty well what you are getting. The camera sometimes picks up colors that are only minimal, while ignoring the feature colors.

黑色蛋白石亮度和身体色调指南蛋白石体色调指南由澳大利亚蛋白石协会设计和创建,并作为Black OpalBoulder蛋白石的指南。蛋白石行业最近也将此指南用于许多蛋白石类型,包括埃塞俄比亚蛋白石

Body Tone N1 - N4 - 用于黑色调身体类型。

身体色调N5 - N7 - 适用于Lightning Ridge开采的浅色蛋白石,但这些较低的身体色调等级可用于Coober Pedy蛋白石和埃塞俄比亚蛋白石。



最亮1至最低7 - 可用于任何蛋白石,平均亮度为3.5,适用于许多被视为商业级的蛋白石。

亮度低于3 - 被认为是B级蛋白石或低商业级。










圆形: 5毫米和6毫米

椭圆形: 6 x 4,7 x 5,8 x 6,9 x 7,10 x 8,12 x 10,14 x 10,16 x 12,18 x 13,20 x 15,25 x 18,30 x 22, 40 x 30。



Opal设置中有一些有趣的神话。有些人认为Opal Doublets和Triplets总是被置于完全支持的设置中以隐藏potch支持。其他人认为完全背衬用于保护石头。这两件事都不是真的。一个珠宝商可以很容易地“隐藏”在开放式背景中的双重线,因为石头和背景之间的连接线将被设置的一侧覆盖,使得很难看出石头的背面是否是不同的石头或简单的同一块石头的不太光亮的一面。






该矿工已经拆除了任何黑色蛋白石粗糙 ,他有一个市场,卖给你剩下的东西。通过剪切,您通常可以告诉您将要切割的内容。你仍然必须注意蛋白石的裂缝,因为一旦裂缝变得明显,石头就会失去一半的价值。





并非所有蛋白石都有价值。 Potch,有时被称为“普通蛋白石”,不反映颜色。然而,Potch确实有它的用途,作为双头和三胞胎的支持。当有颜色与potch混合时,它被称为“potch and color”。


某些类粗糙蛋白石不适合制作宝石。有些非常多孔。其他人有白垩的外表。还有一些人可能会在短时间内失去颜色。是的,当凝胶中的水蒸发时,某些类型的蛋白石在干燥的环境中破碎是很常见的。对买家的最佳保护是从知识渊博且声誉良好的经销商那里购买蛋白石,该经销商准确地详细说明您的购买对象并愿意保证这些石头。注意:如果您购买粗糙蛋白石,则无法保证不会破裂。这是你冒的计算风险,也是蛋白石切割“兴奋”的一部分。 蛋白石potch

3.在检查蛋白石首饰时 ,从侧面看石头以确定它是否是三合一。实心和双层蛋白石圆顶简直就是形成弧形圆顶形状的蛋白石。三胞胎有透明的水晶圆顶,以保护平坦的蛋白石表面。




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Over 5 years ago Opal buyers would constantly check and ask questions about Body tone for black opals.
Market trends have now changed, and most buyers ask about Brightness as well as Body tone.
Chinese buyers would only buy N1 body tone black opal and this placed a lot of demand for Body tone ahead of Brightness.
Today Brightness is the most important and has major consideration factor in valuing opals as well as the opal pattern.
Unfortunately we have two systems for Brightness ratings that have not been approved by Cibjo or leading gemmologist organizations.
On Opalauctions we recommend the Australian opal association Opal brightness Guide that places brightest opal at B1. compared to the original B5 rating.

29th Jan

Yes I agree, Brightness should be included on black opal listing.

2nd Jan

Reply Tony translate
Or can we buy the rule Opal base body tone guide SVP
Yes here is link


21st Jan 2017

Ou pouvons nous acheté la règle Opal base body tone guide SVP

21st Jan 2017

Yes.Helped me a lot.Thank you.

3rd Oct 2016

I do get confused with body tone chart with brightness chart.
Its seems everyone states body tone of an opal but I think Brightness is just as important
Lot black opals now seem to be N2 to N3 as an average
I do not see many N1 black opals and they are all expensive now
That’s why I think Brightness is more important now and most are rated B3 to B4
May I make a suggestion that Brightness be added below Body tone on black opal listings

24th Aug 2016
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