What is "precision cutting"?

[ecf8503]

Just testing the waters here on CS...

I'm pretty well versed in diamonds, and I'm trying to learn more about CS. For instance, "ideal cut" in the colorless diamond world implies (in my mind) a nod to light performance - maximizing light return, as well as symmetry. Does this hold true in the CS world as well? Are "precision cut" colored stones cut to maximize color intensity (as with colored diamonds) or light performance? Does that imply symmetry as well?

I have been visiting various CS sites, and I find myself drawn to stones with apparent symmetry and minimal windowing and extinction. Is that essentially what a "precision cut" is aiming to do?

What are some known sites I can shop for / drool over these types of stones? (I've been spending a lot of time on mastercutgems and gemfix already).

Thanks!

 

[boerumbiddy]

There's a wonderful cutter named Uli Zeisberg at www.osirisgems.com in Germany who posted a very informative explanation of precision cutting. Here's the link, I hope.
http://www.osirisgems.com/precision_cutting
It's not so much about light return, though that is a consideration, as it is about perfection in whatever facet pattern is chosen. And of course many colored stones with mediocre cuts are prized just because of their color!

 

[LoversKites]

There's a wonderful cutter named Uli Zeisberg at www.osirisgems.com in Germany who posted a very informative explanation of precision cutting. Here's the link, I hope.
http://www.osirisgems.com/precision_cutting
It's not so much about light return, though that is a consideration, as it is about perfection in whatever facet pattern is chosen. And of course many colored stones with mediocre cuts are prized just because of their color!

I was about to post the same link

 

[chrono]

Simple question with a complicated answer.

Because colour is so varied in the CS world, there is a huge range of colour quality. Add that lapidaries have varying budgets, some can procure nicer rough and some not so nice rough. Having the right contact also comes into play, so some can get better coloured material more easily than others. Precision cutting also comes in varying qualities; some of them are better cutters than others (aka select the best pattern and angles for a particular rough). I've seen precision cut stones with huge tilt windows and extinction due to the incorrect pattern selected.

Precision cutting is about trying to get that perfect balance between bringing out the best colour, best light return and least wastage of rough material (avoiding inclusions, colour banding, pleochroism, etc). A lapidary might use a lighter coloured piece to highlight the contrast pattern better, and another lapidary will choose a checkboard cut to get more flash out of a darker toned material.

This is why the learning curve for buying CS is very steep; there is no one formula or even several formulas to help along the way.

[URL='https://www.pricescope.com/community/threads/can-we-start-a-new-thread-with-respected-cs-vendors.169561/page-5']https://www.pricescope.com/community/threads/can-we-start-a-new-thread-with-respected-cs-vendors.169561/page-5[/URL]

 

[T L]

Just testing the waters here on CS...

Are "precision cut" colored stones cut to maximize color intensity (as with colored diamonds) or light performance? Does that imply symmetry as well?

Thanks!

That's the ideal, but unfortunately, it doesn't always happen. I would also add to Chrono's comments, that I saw a precision cut gem that had its table cut along the less saturated axis, to make it larger. Therefore size was sacrificed for beauty. It was disheartening because the other axis had amazing color. I've seen some that were also precision cut, but would have been far less less extinct if another type of cut was used. Therefore, just because a gem is precision cut, that doesn't mean that the cut was done to best maximize beauty, size and light return. I'm not saying native cuts are better, but one shouldn't assume that because a stone is precision cut, it is cut in a way that maximizes all aspects of beauty. One must make that judgement on their own.

As for symmetry, that is not a requirement. Certain fantasy cuts are not symmetrical at all, like those of lapidary John Dyer.

 

[ecf8503]

Thanks everyone -

It is a steep learning curve I'm seeing, and I'm learning more all the time.

 

[PrecisionGem]

I always thought a "precision cut gem" was one cut by Precision Gem.

Actually I think the term become popular right here on Pricescope, and is now being used more and more outside of this site. Normally in the trade, there are two types of stones; well cut, and not well cut.

 

[ecf8503]

I always thought a "precision cut gem" was one cut by Precision Gem.

Actually I think the term become popular right here on Pricescope, and is now being used more and more outside of this site. Normally in the trade, there are two types of stones; well cut, and not well cut.

Haha! Well see that's what I'm trying to ferret out - how can you tell the well cut from the not so well cut just by 1 or 2 (sometimes not so good) pics? It is difficult with diamonds to tell in a picture unless it is aligned just perfectly and photographed superbly, and even then you can't tell a whole lot about light performance.

Are colored stone photos (as a whole) reliable? If it looks like there is a window or some extinction in the pic is it likely there in real life as well, or is it a photographic illusion?

I've seen many pics of elongated stones (that will naturally produce a bowtie effect), and it appears there is a bowtie there - but how visible is it in reality?

I'm a stickler on cut in diamonds, and I find myself drawn to colored stones with symmetrical faceting - which I know isn't the be all end all, but for me it is a pleasing effect. Scouring websites for symmetrical, well cut stones is a fun but exhausting adventure!

 

[chrono]

I always thought a "precision cut gem" was one cut by Precision Gem.

Actually I think the term become popular right here on Pricescope, and is now being used more and more outside of this site. Normally in the trade, there are two types of stones; well cut, and not well cut.

That's a good one, Gene, and apt too. You are right though, in that there's well cut and not well cut, which makes it much easier to understand.

 

[Jeffrey Hunt]

And with precise faceting now coming from commercial cutting houses overseas combined with some US and Canadian faceters even subcontracting out to these houses, there is definitely a blurring of the terms.

The terms precision cut and commercial cut are becoming one and the same. I agree, there is really only well cut and not so well cut! The style of cut can absolutely vary though.

Jeff

 

[chrono]

Circe,
You should have come straight out with your questions so that I need not be so generic.

Some flaws are easier to spot than others. A straight on photo is best and the easiest to make a correct judgment. Some vendors try to hide cut issues by only taking pictures of the gem at an angle. Straight on allows one to spot any potential windowing issue or uneven colouration (colour banding or zoning, not to be confused with contrast scintillation).

Tilted gives an idea how large the tilt window is (and whether you can accept that level of tilt window). Tilt window is normal and to be expected but it will be smaller or larger depending on the RI of the gem, the angle of the gem vs the camera, and the cut quality. A profile view is a bonus to gauge crown height, fat/shallow pavilion, off-centered culet and any inclusions which might be reflected from the top view.

For the most part, photo is quite reliable if you know what to look for. It's not foolproof and like diamonds, videos are more accurate than pictures. Photos are the first step in the elimination process. If there is a window in the picture, you will see it IRL. If there is extinction in the picture, you will see it IRL (not to be confused with camera obstruction or head shadow which goes away if you get your face further than 8 inches away from the gem). Again, how obvious it is to you will depend on how acute your vision is and how well your eyes are trained to pick it up.

How much these factors will bother you is a different thing than how well you can spot them. I can spot small windows but can overlook them in special cases (price factor, commonness of the gem, rarity of colour, etc).

As with diamonds, we all aim for gems with minimal bowtie. The effect tends to be stronger or more obvious when a gem has a light colour, less obvious when a gem has a darker colour. Like diamonds, it is more easily seen under certain lighting, less obvious under certain lighting. Sometimes, the bowtie will look dark and sometimes it will become the brightest part of the stone.

 

[T L]

Tilted gives an idea how large the tilt window is (and whether you can accept that level of tilt window). Tilt window is normal and to be expected but it will be smaller or larger depending on the RI of the gem, the angle of the gem vs the camera, and the cut quality. A profile view is a bonus to gauge crown height, fat/shallow pavilion, off-centered culet and any inclusions which might be reflected from the top view.

Even with low RI stones, you can minimize the tilt window by making certain crown angles. I was told this by Barry Bridgestock.

I think a high crown and small table tends to minimize windows in low RI stones. Someone please correct me if I'm wrong.

 

[Michael_E]

Even with low RI stones, you can minimize the tilt window by making certain crown angles. I was told this by Barry Bridgestock.

I think a high crown and small table tends to minimize windows in low RI stones. Someone please correct me if I'm wrong.

This is correct. Small tables are probably 70% of this effect with crown angles being more important as the R.I. of the material decreases. The shape curvature of the stone also plays a large part in this, as stones with broad areas of curvature, (or flat, as in emerald cuts), show more of a tilt window on those broad curved sides. Triangular cuts show this very well in low R.I. material, since they have three rather broad curves.

Tilt windows are not ALL bad though. With the right setting they can add to the effect one is trying to achieve.

 

[ecf8503]

Circe,
You should have come straight out with your questions so that I need not be so generic....

Thank you for explaining, even if it is "generic" (and even though I'm not Circe! )

I'm enjoying learning about all of this. Just wondering if I can trust my eyes when it comes to pictures. I haven't taken a financial leap yet, and trying to find a suitable first project is fun, and when I do it will be interesting comparing what I see in person with what photos show. Lucky for my pocketbook, I tend to be drawn to unusual, and apparently less valuable, shades.

 

[chrono]

ECF,
I am so very sorry to have mistaken you as Circe. The blue fluorescence of your avatar threw me off because I'm used to seeing her blue avatar in Hangout, so the two went hand in hand automatically in my mind. Again, my apologies. Given time, you will get better and more confident in your gem photography interpretation. Some vendors are much better than others (or rather more well known than others) for taking accurate pictures.

 

[ecf8503]

It's ok - I know I'm not the only one w a fluor stone for an avatar! Thanks for the help -