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Author Topic: Finished opal sizes?  (Read 527 times)

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Pusscat

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Finished opal sizes?
« on: August 31, 2017, 07:20:51 AM »

Although I'd love to be able to go from cutting rough opal through to designed mounts and ending with a great set piece, my skill set isn't there. (...yet) so I'm concentrating on the stones.

I know it's a bit of an open ended question, but when you're cutting opal, what sort of depth do you aim to for the sides?  I'm sort of going for min 2 mm if the stone is small, but I'm not sure what would be considered too deep?

Also, I tend to cut a shape depending on the fire in the stone rather than making calibrated shapes.  I tend to try and make them aesthetically pleaseing shape wise but are there shapes that people tend to use / not use for opals?

Any advice would be welcome!
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vitzitziltecpatl

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Re: Finished opal sizes?
« Reply #1 on: August 31, 2017, 08:32:26 AM »

Your 2mm size for small opals is fine. On the "deep" end you can do whatever you want if you have a jewelry design in mind for how it will be set. The face size will figure in to how thick you want it. Just keep an image in mind of a typical slab of other types of rough. They're usually 5-6mm these days. Hope this helps.

hummingbirdstones

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Re: Finished opal sizes?
« Reply #2 on: August 31, 2017, 08:39:49 AM »

Also, if the cab ends up a bit thick for a particular setting, it can always be taken down a tad to make it fit.   On the other end, if it's a bit too thin, it can be shimmed up in a setting.  :icon_sunny:
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Robin

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Re: Finished opal sizes?
« Reply #3 on: August 31, 2017, 03:48:24 PM »

Not sure what others do, but what I have done in the past goes something like this:
1. Inspect rough for obvious color bars
2. Once you've determined where the fire is, remove any deposits on the face of it that might be there, but do so slowly.  The objective here is to expose the color so you can go to step 3
3. Judging by the way the fire is, and taking into account any inclusions that might exist, work out the basic shape that you want to end up with.  If you are going to do a calibrated size, make sure you mark the area 1mm or more larger than the final size.
4. If it's a larger stone, and you have a trim saw, sometimes it helps to use the saw to remove larger pieces of material.  2mm and 3mm may seem small, but if you can trim off excess and still get an opal out of the excess, you're ahead of the game as to if you just grind it all off.
5. At this point, you can take the thickness into consideration.  You have to remember that when you dome the cabochon, it's going to take off a small amount on the top, but more on the sides, etc.

High and medium dome cabochons are easier to deal with in regards to thickness, but with low dome ones you will want less of a dome shape and more of a low dome with a rolled edge (otherwise you wind up with easily chipable edges)

On the large end of things, if you have a cabochon that is 3cm x 4cm or something, it doesn't need to be 2cm thick, but you're not going to want to do a medium/high dome on something like that either.  Just go with a low dome, save as much fire as you can, and then leave it in a thicker state with the very edges nearly vertical, but bevelled/rounded to meet the edge of the dome.

The main thing I go for when cutting where thickness becomes an issue, is to get the face of the cabochon looking how I want, along with the overall shape of the stone, and then after it's face is polished up to 3k, I'll take material off the back if needed.

Never grind away fire to make a stone thinner. :)

As Robin said, if you have no choice but to cut a stone thin, you can place other material between it and the inside of a setting, though if you have a super thin opal that has some transparency to it, you might consider getting some basalt, jet, or other black backing stone, and make it a doublet.  Then the stone you add is up to you for thickness.   From personal experience, you *can* use black jade as a backing stone, but you're basically gluing a fragile Mohs Scale 5.5/6.0 stone, to what is considered by some to the be the toughest stone on earth.  As a result, grinding can yield some less than desirable results.

Final note:  I'm not a pro by any means, just speaking from personal experience.
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55fossil

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Re: Finished opal sizes?
« Reply #4 on: August 31, 2017, 06:39:56 PM »

   Cut for COLOR....  If it is cheap opal or just an average stone it really is not that important. You can cut what pleases you. If it is an opal solid with really good fire then you take your time. Examine the stone and cut for the best color. Weight and shape also add or subtract value, but it depends on who your market is. Your average consumer is not going to pat big bucks from someone they do not know selling on e-bay or etsy. An established cutter gets a lot more money as a rule because of the trust factor unless it is top 5% gem material. Even a Spencer Opal triplet can command high prices if:  the color is intense and multi-color: it is a good size and a pleasant shape, the work is flawless. But it will not get the thousands of dollars a top gem Australian opal will command that is similar.
PS:  premium opal triplets can be purchased at the Dealers Show in Tucson for $15 to $40 that are incredible. With opal solids just add zeroes.....
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gemfeller

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Re: Finished opal sizes?
« Reply #5 on: August 31, 2017, 07:19:09 PM »

Unless you're prepared to develop the skill set needed to fabricate or design and cast your own settings, you're pretty much stuck with the typical rounds, ovals, rectangles, cushions, triangles and pear shapes found in off-the-shelf calibrated settings.  Very few such settings are made with opals in mind in the U.S., don't know about Old Blighty.  I think I see more rounds, ovals and pears than other opal shapes in jewelry stores here. 

The required depth of the stone is proportionate to the size of the stone, the nature of the rough and the mechanical requirements of the setting, including whether it will be prong or bezel set. Color, directionality of the play of color and brightness are always the foremost concerns. For instance, I've found that strongly directional stones can sometimes be very effective in pendants but not so much in rings.  Many opals simply won't allow cutting to that trio of ideals due to the nature of the rough.  In those cases doublets or triplets are considerations.

Having made my own settings for years I've come to think of the end design and possible setting methods during the cutting process, and cutting with those ends in mind.  It's probably the reverse of how most cutters think until they are able to control the entire process.  I think your approach is sound and you're asking the right questions.  Best wishes for success.
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Pusscat

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Re: Finished opal sizes?
« Reply #6 on: August 31, 2017, 10:56:42 PM »

Thanks for the really helpful info everyone....love this website, people are so open and willing to share experience!

I would like to get into producing my own settings and that will probably happen. I see it as the next step.

ASO

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Re: Finished opal sizes?
« Reply #7 on: September 12, 2017, 01:08:03 AM »

It all depends what type of jewelry its going into and how the opal will be set.  When I sell cut stones I recommend ways to safely set the stone and show how it should be orientated or faced in the jewelry.  3/3.5mm is very common in opal but I have cut good stones that are only 1.5mm thick that should be set using epoxy, all the way to over an inch to be set with prongs.  If your setting thinner stones I would use a thin bezel rather than a thick one less pressure is needed in setting.
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