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 Post subject: What is the ideal baguette cut?
PostPosted: Thu Apr 25, 2019 3:24 pm 
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We know there is an ideal round cut for diamonds described by Marcel Tolkowsky. He defines all the angles and the proportions for the crown, table and pavilion.

I am trying to find what would be the ideal cut for a baguette diamond or colored stone.

I am only interested in an ideal baguette cut.

I could not find many technical drawings for a baguette cut. I only found this:

http://www.facetdiagrams.org/database/files/pc12001.html

My question is, is this the ideal cut? How many facets should a ideal baguette cut have? What should be the crown and pavilion angles?

But the most important question I have is what should be the pavilion height? The above example defines pavilion height as 53.6%. Why is that? How was it determined? Is it ideal?


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Sun Apr 28, 2019 10:00 pm 
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From what I understand, Tolkowsky's Ideal Brilliant cut is a brand cut that had good performance.
Due to being marketed well and vetted by other cutters it came to be used as a standard for other round brilliants for a time.
The problem is that those proportions rely on the fact that the mains facets meet the girdle, and step or horizontally split facets can't do that by definition...

In addition, the goals for step cuts tend to be different to rounds, things like uniform patterns seem important to Asscher cuts, and baguette cuts are used as accent stones a lot. Colour intensity is often prioritised over brilliance, too.
What would you want to see in your Ideal Baguette?

My own experiments with rendering step cut designs has shown that the proportions given in instructions very rarely give the best results in my eyes, and are often chosen to make the diagram look even, or for best yield in the chosen material.
I think Long & Steele's baguette is proportioned to make the mains equal in size to the table, and you can find a lot of emerald designs proportioned to so the step tiers are of even width when viewed from the bottom.

I wouldn't trust a design's proportions without rendering it first, especially when a change of 0.1 in refractive index can mean the reflection pattern given is significantly altered. The number of facets would mostly depend on the size of the stone to me.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Wed May 08, 2019 1:51 pm 
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Shifter55 wrote:
I think Long & Steele's baguette is proportioned to make the mains equal in size to the table, and you can find a lot of emerald designs proportioned to so the step tiers are of even width when viewed from the bottom.


Thank you for your answer.

Can you elaborate the above quote:

I know what table is but what are you referring to with "mains"?

When viewed from bottom the dimensions of the step is not exactly the same as the table:

Table: 0.491x1.491 where as Bottom view step: 0.445548838x1.445548597

So slightly different.

Do you have other baguette cut diagrams I can look at?

My question is why did Long & Steele choose 41.00° and 51.00° for their pavillon angles and why did they choose pavillon height as 53.6% of Width? (P/W = 0.536)


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Wed May 08, 2019 6:30 pm 
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I think using the term "ideal" to describe the cutting of a baguette is meaningless.
The term is thrown about to describe the cutting parameters of a round brilliant diamond for maximum brilliance and dispersion.
Even with a round, brilliant diamond it is a misleading concept, let alone with colored stones all having different optical properties.
Dr. Mary Johnson wrote:
The notion that there’s something special about one set of proportions which is not produced by another set, just doesn’t hold up


Maximum brilliance and dispersion is not really an option with these long, narrow, step-cut slivers.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Fri May 10, 2019 7:11 am 
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VFA wrote:
I know what table is but what are you referring to with "mains"?

Do you have other baguette cut diagrams I can look at?

The mains facets are the last set of facets on the bottom, before it ends at the culet.
As for more cuts of this sort... Jeff Graham's Easy Emerald Article is informative:
http://www.jewelcutter.com/graham/desig ... rald.shtml

Shor International's faceting instructions page has a table of angles for step cuts that ensure even patterns in the stone - although, all but the rightmost Group C angle require some tweaks to get the best results, a render of the said design is attached below.
https://www.ishor.com/faceting-machine- ... 0Group%20A

On this forum I recommend searching for "asscher" in posts authored by "ROGER DERY", he is a master of step-cuts and a lot of his angles given create even patterns when rendered.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Fri May 10, 2019 6:02 pm 
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Barbra Voltaire wrote:
I think using the term "ideal" to describe the cutting of a baguette is meaningless.
The term is thrown about to describe the cutting parameters of a round brilliant diamond for maximum brilliance and dispersion.
Even with a round, brilliant diamond it is a misleading concept, let alone with colored stones all having different optical properties.
Dr. Mary Johnson wrote:
The notion that there’s something special about one set of proportions which is not produced by another set, just doesn’t hold up


Maximum brilliance and dispersion is not really an option with these long, narrow, step-cut slivers.


All your points make sense to me.

Tolkowsky determined and formulated all the angles and dimensions for the ideal cut for a round brilliant diamond to maximize fire, brilliance and scintillation of the diamond.

The baguette cut diamond which I am interested in by nature cant be as brilliant as a round diamond.

However I believe just as the ideal cut for a round diamond we could define an ideal cut for baguette cut. Even the baguette cut has some fire and brilliance. There must be some ideal angles and dimensions for the baguette cut that would maximize brilliance.

I am aware baguttes are mainly not for brilliance but rather to show the color, clarity or internal flawlessness of the stone. What about dimensions and angles to maximize those?

Assuming we want to determine an ideal baguette cut for a diamond (RI = 2.4)

Just looking for the ideal pavillon angles and pavilion height for a baguette cut diamond.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Fri May 10, 2019 6:03 pm 
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Shifter55 wrote:
VFA wrote:
I know what table is but what are you referring to with "mains"?

Do you have other baguette cut diagrams I can look at?

The mains facets are the last set of facets on the bottom, before it ends at the culet.
As for more cuts of this sort... Jeff Graham's Easy Emerald Article is informative:
http://www.jewelcutter.com/graham/desig ... rald.shtml

Shor International's faceting instructions page has a table of angles for step cuts that ensure even patterns in the stone - although, all but the rightmost Group C angle require some tweaks to get the best results, a render of the said design is attached below.
https://www.ishor.com/faceting-machine- ... 0Group%20A

On this forum I recommend searching for "asscher" in posts authored by "ROGER DERY", he is a master of step-cuts and a lot of his angles given create even patterns when rendered.


Thank you for those links. They are helpful.

Shor's instructions state that:

The pavilions of step-cut stones should be given a depth of 50%-70% of the girdle diameter (or girdle width)
The depth of the pavilion should be minimized to maximize the amount of light returned.
To do this, It is important to keep pavilion facet angles as low as possible.
It is difficult to cut facets accurately if the change in the angle is less than 4° for each step.
Never cut a pavillion facet at less than the critical angle

Comparing this to Long & Steele's baguette cut: http://www.facetdiagrams.org/database/f ... 12001.html

Shor's illustrations have 3 and 4 step pavilion. 2 step pavilion would minimize pavilion height as Shor instruct us to do. What are the advantages of more than 2 steps? Is 2 steps ok?

L&S's mains start with an angle 41 (which is good as its above the critical angle for the majority of gemstones) and go upto 51 degrees for the next step instead of increasing by 4 degrees as suggested by Shor. 51 degrees could be made smaller to minimize pavillion angle. Why wasn't it?

Should the height or the width of the steps be equal? Neither are equal for Long & Steele's baguette cut.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Fri May 10, 2019 8:23 pm 
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The ideal cut for a baguette is diagonal slices of medium thickness, slathered with garlic butter and toasted golden
DANG IT

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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Fri May 10, 2019 11:44 pm 
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Kidding aside, Stephen...that's the best answer. =D> =D> =D>


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Sat May 11, 2019 3:55 am 
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Understand that the Tolkowsky "Ideal Cut" is a set of compromises between, brilliance, dispersion, and scintillation (pattern) calculated by mathematician Marcel Tolkowsky to produce the most attractive round brilliant cut in his opinion. The term "Ideal Cut" was a trade name than Lazare Kaplan (Tolkowsky's cousin who had requested the calculations) came up with to market stones cut to this standard. It is really a marketing thing of a particular, innovative, diamond manufacturing and dealing company Lazare Kaplan International. Back in the day attempts were made to enforce the trade mark "Ideal Cut" by LKI. I think these days it has evolved into common usage. Also, one needs to understand that there has always been a disagreement in the industry over what proportions were best. Table size seems to be the proportion that people most often disagree on.

https://lazarediamonds.com/AboutUs/OurHistory

I think it better to view best angles and proportions for a Diamond is to follow the ranges of cut properties encapsulated in the GIA Excellent standard. This is the result of study and testing on many of thousands of RBC stones. This testing included a lot of subjective testing in addition to mathematics. They put stones of various proportions in front of people including cutters, dealers, consumers, and asked them to tell them which was the most attractive.

Gia offers a computer program that helps you determine and grade all of the various properties of cut and proportions on round diamonds in order to come up with an overall cut grade. This only applies to RBC diamonds.

https://www.gia.edu/facetware-help

OK, now that we have done away with the misconception of mathematically perfect proportions, lets try and get a handle on the question in front of us.

There is no reason that the same angles and proportions used to cut a round would not perform just as well in a baguette cut. The material properties of diamond, and Snell's Law don't change with shape. This takes care of brilliance and, dispersion. In industry practice this is almost never done as yield figures more prominently as a criteria in fancy shapes, because the "Ideal Cut" marketing was never applied to them. (GIA is currently working on defining "Excellent" for fancy shapes).

Now we have to look at "scintillation" or pattern. This will actually be a pretty subjective. It will be controlled mostly by the how you size the tiers of facets on the pavilion and crown to create a pleasing pattern.

So my suggestion is to keep the pavillion main angle between 45 and 40 degrees, but the minimum pavillion angle at least 1 degree above the critical angle. Keep the crown height in proportion to the same as an Excellent diamond. Finally size the facet tiers in classic emerald cut relationship.

You well end up with a fine looking baguette cut stone, but it will not taste as good as Stephens solution.....


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Sat May 11, 2019 2:03 pm 
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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Sun May 12, 2019 2:58 am 
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VFA asked specifically about a diamond baguette cut, so it may be appropriate to see what Basil Watermeyer (Diamond Cutting) has to say about it.

"Baguette: A word of French origin and used for describing small, fattish rectangle cuts. They can have as few as 4 breaks [facets] on the crown and 8 on the base, with no girdle facets. Angles and table proportions normally mean nothing." (p. 282)

On page 298 Watermeyer gives the facet angles for 'life' in an emerald-cut diamond, and you could use those for a baguette. Table: 59-62%; Base: 3 tiers at 37, 41-42, 52-54 degrees; Top: 32, 34.5, 40 degrees. Arrived at through many years of experience, this probably is as close to an 'ideal' diamond step cut as one can get.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Sun May 12, 2019 6:41 am 
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Duncan Miller wrote:
On page 298 Watermeyer gives the facet angles for 'life' in an emerald-cut diamond, and you could use those for a baguette. Table: 59-62%; Base: 3 tiers at 37, 41-42, 52-54 degrees; Top: 32, 34.5, 40 degrees. Arrived at through many years of experience, this probably is as close to an 'ideal' diamond step cut as one can get.

This is what those angles give me when rendered, all tiers on the top and bottom were cut to equal size. Feels like one too many crown tiers to me, but there's plent of scintillation in the table (and fisheye)!


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Sun May 12, 2019 10:17 am 
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Fisheye is usually ascribed to a stone where there is light leakage attributed to cutting below the critical angle of the material. That is not the case if the RI is that of diamond, and the angles stated are used.

I think the effect you are seeing in this stone is most likely the reflection of the table in the stone caused by angles that are not working well together.

The solution to these two performance issues would be entirely different.

Try not cutting the tiers to equal size. The tier at the girdle should be the widest, the tier at the culet should be the narrowest, and the tier in the middle proportionally between these sizes. The same pattern should be followed on the crown. Then play with the table size to minimize the black band cause by it's reflection.


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 Post subject: Re: What is the ideal baguette cut?
PostPosted: Mon May 13, 2019 4:02 am 
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Shifter55 wrote:
This is what those angles give me when rendered, all tiers on the top and bottom were cut to equal size. Feels like one too many crown tiers to me, but there's plent of scintillation in the table (and fisheye)!

What you have rendered is not a baguette cut, but an octagonal step cut. A diamond baguette is a rectangle with sharp corners (vulnerable to chipping).


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