3 Tier Pavilion Mains in Tanazanite or Sapphire / Why?

[ChunkyCushionLover]

I am puzzled why I see this type of pavilion facet design.
Surely it can't be just to save weight with a pavilion bulge.

It seems to be most prevalent in darker tone material like tanzanite and sapphire and perhaps used to enhance saturation where one has lighter material than they would like.

The negatives seem to be both a window and potential extinction areas and a loss of brilliance.

I would love to hear a precision cutters thoughts or anyone's on why this design is chosen and how it could be done differently.

Also if anyone could point me to that thread precision versus native cut thread I would be appreciative.

 

[ChunkyCushionLover]

 

[Jeffrey Hunt]

Doug Menadue of Bespoke Gems has a beautiful well informed web page on the subject of native cuts. It's well worth a visit.

http://www.bespoke-gems.com/SacredGeometrics_Page_WhatToLookFor.php

Kind Regards,

Jeffrey Hunt

 

[ChunkyCushionLover]

I am puzzled why I see this type of pavilion facet design.
Surely it can't be just to save weight with a pavilion bulge.

It seems to be most prevalent in darker tone material like tanzanite and sapphire and perhaps used to enhance saturation where one has lighter material than they would like.

The negatives seem to be both a window and potential extinction areas and a loss of brilliance.

I would love to hear a precision cutters thoughts or anyone's on why this design is chosen and how it could be done differently.

Also if anyone could point me to that thread precision versus native cut thread I would be appreciative.

Thanks Jeff that is a basic answer but I'm looking for a lot more .
It would seem to me, as a novice just starting to understand the weight/color/brilliance tradeoff, if the goal was the most brilliant stone instead of the weight saving "goldfish belly" one would cut the pavilion mains from culet to girdle using the optimal angle for the RI. So for the tanzanite above the critical angle of ~36 so ~39 - 41 degree pavilion mains.

The basic diagram I posted was for quartz from Richard Hughes Ruby and Sapphire, where the critical angle is over 40 degrees so the optimal angles are above this.

 

[Jeffrey Hunt]

It would seem to me, as a novice just starting to understand the weight/color/brilliance tradeoff, if the goal was the most brilliant stone instead of the weight saving "goldfish belly" one would cut the pavilion mains from culet to girdle using the optimal angle for the RI. So for the tanzanite above the critical angle for zoisite is = 36.39 so a ~39 - 41 pavilion mains.

HI ChunkyCushionLover

I'm sorry I wasn't able to answer your question. The Bespoke pages are a basic introduction to some of the differences between native cuts and custom cut stones.

It's important to keep in mind though, the goal is not always the most brilliant colored stone. If you are willing to dig through the archives of Gemology Online, USFGfaceterslist and even Northcoastfaceting - with a recent discussion of the best quartz angles for a round brilliant, you will find a wealth of information that will hopefully answer your question. There is sometimes conflicting information too - not all faceters agree on "correct" or optimum angles. It depends on the desired gem and faceting process.

Faceting styles and preferences will vary between cutters. Consider the Asscher cut. Even this design has different styles among the faceters often mentioned on Pricescope. Five tiers or four, windmill pattern or no, large gem or small, high refractive index or low. There are more variables.

Kind Regards,

Jeffrey Hunt

 

[LD]

CCL I believe that this is done to preserve weight and maximise cost (usually, but not always, at the expense of beauty). I've seen this commonly with sapphires, tourmalines, spinel and tanzanites also but surprisingly with lower cost gems too. I guess if you achieve nudging over the carat or half carat mark it can make a difference to price. I don't think anybody would intentionally cut this way if attempting to achieve a stunning gemstone!

 

[PrecisionGem]

A lot has to do with speed of cutting and being able to work out a design that gels together. A step cut can be fashioned with most any design. It's quick to to on simple equipment.

 

[zeolite]

Surely it can't be just to save weight with a pavilion bulge.Yes, that's exactly why its done. Another reason may be that primitive jam peg machines can’t cut steps are as close to each other in angle, as precision machines.

It seems to be most prevalent in darker tone material like tanzanite and sapphire and perhaps used to enhance saturation where one has lighter material than they would like. Yes, the pavilion bulge will darken lighter material, at least until they window the bottom row of facets

The negatives seem to be both a window and potential extinction areas and a loss of brilliance. Yes that’s exactly what happens.

From the Bespoke link:

Remember that the main aim of the commercial cutter is to maximize yield. Stones are sold by weight (carats) so the more stone they have, the heavier it is, the more money they make. These goldfish cuts are very prone to windowing as you can see in the following example... all the light just goes straight out the bottom.

The essence of the gem cutter's art is to get as much light as possible to return back up through the top of the stone to your eye.
This last sentence should read: “essence of the Western precision gem cutter's art …”

I was invited into North Vietnam in the 1990’s to set up a ruby cutting factory, in a remote location near the Laos border. I was the first American to show up there since the Vietnam war. I had some discussion with some Thai trained cutters. They honestly believe that their way, to maximize retained weight, and totally ignore brilliance or fine polish, is the best way. They think American style precision cutting is wasteful and not attractive.

 

[Michael_E]

This diagram is NOT correct and is probably what is causing you some difficulties in understanding CUT in gemstones. The steep sided area in the pavilion has ZERO to do with extinction and in fact is a beneficial trait in many modern designs such as all barion style cuts. The reason for this is that the crown facets bend light entering them inwards so much so that most of the light entering the stone never touches those steep sides. Likewise that area of windowing is only a window directly under a flat crown. All stones will show windows when cut this way...but only under the table, so if the table is small, so is the window.

Then there is the misunderstanding that most people have, probably from looking at diagrams like this, that the light rays entering a stone only bounce directly across and then back out of the stone in one plane. It's just not so. There are many areas in most stones in which the light entering the stone hits a pavilion facet at such an angle that it may bounce across the stone three, four or even more times before leaving the stone. In fact one good way to avoid seeing your reflection in a stone, as well as reducing the size of tilt windows, is to make sure that their are as few facets as possible directly opposite each other and in the same reflection plane, in the pavilion. I have a feeling that many of these "native" step cuts do this more as an accident than by design.

Why three tiers? Because it's the easiest and fastest cut style available to them. Remember that these guy's are cutting upwards of 30 stones per day and have to just ZIP them out or they don't make anything.

 

[LD]

Why three tiers? Because it's the easiest and fastest cut style available to them. Remember that these guy's are cutting upwards of 30 stones per day and have to just ZIP them out or they don't make anything.

Michael - as a comparison, how many stones would it be possible to precision cut in a day please?

 

[PrecisionGem]

I can cut a small round stone, if everything goes perfectly, and I really rush in around 1 hour. Most stones from start to finish, including figuring out what approach I'll take to the stone, the best design etc, takes around 3 to 4 hours. So if I worked a full 8 hours cutting, didn't crap around on the internet, I could get maybe 3 stones a day out. I too have been told by a Chinese guy who runs a cutting house that his workers must cut 30 stones a day. Now they do it a bit differently than we do. Each stone is worked on by several people. One guy only dops and shapes, then passes the stone down to another who cuts and polishes the facets (all in one operation) then on to anther who transfers the stones and the same process continues for the crowns.

 

[LD]

I can cut a small round stone, if everything goes perfectly, and I really rush in around 1 hour. Most stones from start to finish, including figuring out what approach I'll take to the stone, the best design etc, takes around 3 to 4 hours. So if I worked a full 8 hours cutting, didn't crap around on the internet, I could get maybe 3 stones a day out. I too have been told by a Chinese guy who runs a cutting house that his workers must cut 30 stones a day. Now they do it a bit differently than we do. Each stone is worked on by several people. One guy only dops and shapes, then passes the stone down to another who cuts and polishes the facets (all in one operation) then on to anther who transfers the stones and the same process continues for the crowns.

Thank you Gene for the information - fascinating.

Sooooo, building on what you've said, each Chinese guy would only be taking part in the process (which could be 4 or 5 employees deep) so in effect to see what they could produce if they were doing as you are (i.e. start to finish) 30 isn't a realistic number? It would be more like 5-7 if they did start to finish? Even 7 compared to an average for you of 2 per day (assuming 3 or 4 hours) is an incredible increase! It makes sense how these "native" cut gemstones are going to be less precise because even if you look at the time it takes to produce a person will undoubtedly be less accurate as it will be more rushed - and that's not even taking into consideration the fact that they use different equipment etc etc.

 

[PrecisionGem]

I don't think one could cut 30 stones in 8 hours. Maybe they work a 10 or 12 hour day. Many of these shops are what in the west we would consider sweat shops, with much of the work force under 18 years old. If they are dopping (the process of holding the stone to the dop stick) with wax, then there is a certain amount of time it takes for the wax and dop to cool. If using glue, then the again there is a waiting period. The stone gets dopped 2 times. 30 stones in 8 hours would be 16 minutes per stone. Leave maybe 6 minutes total for cooling of the wax, that's only 10 minutes to cut the stone. Don't expect much precision in 10 minutes.