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How To Cut Black Opal
如何切黑蛋白石
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how to cut black opal

This is a great guide for cutting Black Opal. This article contains thorough information from an expert opal cutter, who has a strong passion for black opals and has been in the trade for many years. He provides information on all the necessary equipment needed to cut black opal. See an inside perspective of cutting, shaping and finally, polishing. There is a special section on tips and tricks for cutting a black opal the best possible way. Black opal is considered to be the ‘Queen of Gems’. Historically, it is highly sought after by kings, queens, emperors, maharajahs and sultans. Its’ unique beauty is something to be marvelled. This guide is perfect for all levels. If you are a beginner black opal cutter, it has pictures for every step of the way, however If you have been cutting for a while, it can still be very helpful to refresh your opal cutting knowledge. We hope you enjoy this guide.

Equipment to cut Australian black opal

What You Need to Start Cutting Black Opal

  • Dop Sticks 
  • Trim Saw with thin blade (optional but very useful) 
  • Strong glue or Dop wax 
  • Diamond grinding wheels ranging from 80, 220, 600, 1200, and 3000-grits 
  • Blade (with rim thickness approximately. 0.02”) 
  • Polishing Disk 
  • Rough Leather 
  • Lamp (with 100-watt bulb) 
  • Tin Oxide Polish 
  • Dust mask, Old work clothes and Safety glasses
  • Water supply (Many cutters do not use enough water while cutting and polishing boulder opal )

Cutting a black opal nobby

Cutting a Black Opal Nobby With a Porcelain Top

This is a natural nobby from Lighting Ridge Australia. It has been rubbed down by an opal miner to expose the bright flashy blue opal color bar. The opal rub originally weighed 50cts and it cut to a beautiful 9.10 carat N1 black opal.

Rubbing down 50 carats rough black opal knobby on an opal cutting machine

The white porcelain top has to be rubbed down to expose the colour. White porcelain tops are rare and most of the time the opal will show bright electric blues.

Shaping the black opal on cutting wheel 600 grit

We have an old Gem master cutting machine that is around 20 years old and it just keeps going.

Cutting of the white potch

First Step - Rub Off The White Potch

With black nobbies it is important to find which side is up or down. Sometimes it can be very tricky if both the sides are black potch. If you purchase a parcel, always cut the lowest grade first and avoid cutting the rough with the most potential until you fully understand how the rough faces. If you only have one piece of rough, it is best to cut and work a small edge to see how the colour exposes itself.

Final polishing black opal on resin wheels

While rubbing down this nobby on a 400 grit diamond wheel you can see the color darkening inside this white potch. Using a 240 grit wheel is also fine for this stage. Just don’t press the opal too hard against the wheel or it could crack. Let the wheel work for you and always have plenty of water. Shape the opal on the 800 grit diamond wheel. Shape the stone by hand with a firm grip.

Dop the opal for cutting and polishing

Second Step - Dop The Opal

Place the opal on a dop stick so it is easier and more accurate to shape and polish. You can use a quick drying super glue to stick the opal on the dop stick and when you are finished cutting you can place the dop in the freezer for few minutes and stone will flick off easily.

finished polished and shaped  910 carats black opal

We have used green jewellers wax and a small methylated bunsen burner. Quickly heat the back of the stone so it is dry and then heat the wax and slowly drip or smear onto the opal. Than you just need your fingers to rub around edge to make a smooth finish. Many cutters burn their fingers doing this and it does take practice. Now with the dob stick you can control, shape the opal and start getting it ready for polishing.

shaping the black opal

Third Step - Final Shaping

On the last diamond cast wheel it is recommended to do some quick turns. This will ensure an even curved surface on the opal. A good way to see if there are any scratches is to hold the opal up to the light and roll backwards and forwards so the scratches are more visible. The polishing stage starts with a rubber polishing wheel that has 1200 grit and then 1800 grit. Keep plenty of water on the opal and twist opal frequently as they can heat up on these rubber wheels if pushed too hard.

polishing the black opal

Fourth Step - Final Polish

The final stage is to use a lapsa polishing powder. Pig leather can be used for this or the new gemshow lapidary polishing disk. Use a small amount of polish and be sure to remove all scratches.

black opal rough

 

 

tricks for cutting black opal

Tricks to learn when Cutting Black Opal

SEDA OPALS

Cutting challenge - this firey black opal rub had black potch in the face which was slowly rubbed off. I had expected to cut a pendant stone but the opal told me where to cut. The sand spot was deeper than I thought and at the edge of the stone the black potch started to appear and would grow bigger if i continued polishing. Instead of a pendant stone i got a stunning black opal ring stone with a lot of fire. It is such a pleasure to cut stones like this!! 

VIEW THREE ROUGH BLACK OPALS BEING CUT OPEN EXPOSING STUNNING OPALS

Black opal that has been mined at Lightning ridge is cut and polished in a similar style to all other opals. The most important aspect of black opal is to determine which side of the opal to cut. This may seem basic information but it is the most common mistake cutters make.

After purchasing a parcel of rough opal, never cut the most promising piece of rough opal. Always start on small pieces so you understand how the opal will cut. Start by rubbing a small corner of the piece to determine which side faces the best. Some grey rough will have a black centre so also rub on the grey pieces before you start on the black.

If you have large pieces of crystal opals they will sometimes cut better display colour if cut at an angle. There is alot of trial and error and no set rules with rubbing black opals. Except use common sense when cutting black opal. Cut small pieces and understand how the parcel will cut.

Even on the opal fields some opal mines will vary on composition on each layer as opal mined 20 feet down might be different to opal mined 40 ft down.

Another problem new cutters come across is that their new polishing wheels are too sharp and rub away the thin colour bars on black opals. I have seen an $800 parcel rough cut with sharp grinding wheels and only end up with a  $200 stone as the colour was rubbed away.

With new opal cutting equipment it is always best to rub a large rock or a piece of potch against new grinding wheels. Opal cutting equipment can be home made or you can purchase commercial opal cutting equipment.

如何切黑蛋白石

这是切割黑欧泊的好指南。本文包含来自专业蛋白石切割师的全面信息,他对黑蛋白石有着强烈的热情,并且已经在这个行业工作多年。他提供了切割黑蛋白石所需的所有必要设备的信息。查看切割,成型和最后抛光的内部视角。有一个关于切割黑色蛋白石的提示和技巧的特殊部分是最好的方法。黑蛋白石被认为是“宝石女王”。从历史上看,它受到国王,王后,皇帝,大君和苏丹的高度追捧。它的独特之处令人惊叹。本指南适用于所有级别。如果你是一个初学者黑色蛋白石切割机,它的每一步都有图片,但是如果你已经切割了一段时间,那么刷新蛋白石切割知识仍然非常有帮助。我们希望您喜欢本指南。

在闪电山脊开采的黑蛋白石以与其他蛋白石类似的方式切割和抛光。黑蛋白石最重要的方面是确定切割蛋白石的哪一侧。这似乎是基本的信息,但它是切割机最常犯的错误。

购买一块粗蛋白石后,永远不要切割最有希望的粗蛋白石。始终从小件开始,以便了解蛋白石将如何切割。首先,摩擦一块小角,确定哪一面最好。一些灰色的粗糙将有一个黑色的中心,所以在你开始黑色之前也要擦上灰色的碎片。

如果您有大块水晶蛋白石,如果以一定角度切割,它们有时会切割更好的显示颜色。有很多试验和错误,并没有设置规则与摩擦黑蛋白石。切割黑蛋白石时除了使用常识。切小块,了解包裹将如何切割。

即使在蛋白石领域,一些蛋白石矿在每层的成分也会有所不同,因为20英尺以下开采的蛋白石可能与40英尺下开采的蛋白石不同。

新切割机遇到的另一个问题是它们的新抛光轮太尖锐并且擦掉了黑色蛋白石上的薄色条。我看到一个800美元的包裹粗切割用锋利的砂轮,最后只有200美元的石头,因为颜色被擦掉了。

使用新的蛋白石切割设备,最好将新的岩石或一块陶瓷与新的砂轮摩擦。蛋白石切割设备可以自制或您可以购买商业蛋白石切割设备。

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Yannick

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22nd Nov 2020
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