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 Post subject: Microscope Reticle Question
PostPosted: Sun Jan 12, 2020 9:14 pm 
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Greetings!
Has anyone had luck using a microscope reticle to measure a diamond's crown angle?
Or, do you know of any other special methods or tricks for measuring angles?
Thank you and best wishes,
Katy B


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 Post subject: Re: Microscope Reticle Question
PostPosted: Sun Dec 06, 2020 1:34 am 
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The main way I've been doing this if I need to at least get a rough estimate is using the old math way of doing things (SOHCAHTOA). It's not very accurate unless you have a very steady hand or way to get your gauge to be steady. That said if you just want a rough estimate it can get one for you.

You would just need to measurements. Probably the most accurate would be the TOA option so take the height measurement from the girdle to the table and then measure the width distance which would be the edge of the table to the edge of the girdle.

To figure out the crown angle then you would just use:     tan-1(Opposite/Adjacent)
Where Opposite would be the edge to edge measurement and the Adjacent would be the height from girdle to table.

I've attached a quick photo below of what you'd be measuring to use this method. Again, when you have the measurements just use the formula mentioned above. The only way to get a better/more accurate amount is if it's sent out for a diamond report or if you can unmount it then I know there are machines that scan loose diamonds to give you a full cut grading instantly with all the angles and proportions.
Attachment:
File comment: Crown Angle using SOHCAHTOA
Crown-angle Calc.jpg
Crown-angle Calc.jpg [ 348.02 KiB | Viewed 709 times ]


Hope that helps.


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 Post subject: Re: Microscope Reticle Question
PostPosted: Mon Dec 07, 2020 1:26 pm 
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I'm sure that a neater system could be organised with a spare microscope, but in the meantime, this method will do fine.


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 Post subject: Re: Microscope Reticle Question
PostPosted: Mon Dec 07, 2020 5:50 pm 
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Does anyone ever use those old GIA proportionscopes projection setups?

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 Post subject: Re: Microscope Reticle Question
PostPosted: Mon Dec 07, 2020 7:16 pm 
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Stephen Challener wrote:
Does anyone ever use those old GIA proportionscopes projection setups?



I used to use one, back shortly after the Earth cooled and the diamonds were formed.

I can get close enough with the visual reference points as taught by GIA, a table gauge and a crown angle card. It gets tedious as you have to measure all eight mains and average them to get the correct number.

These days if you really want to do a cut grade analysis equal to the labs, you need a machine equal to the labs. That means a Sarin Machine, and GIA Facetware. The best way to do recut estimation as well.


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 Post subject: Re: Microscope Reticle Question
PostPosted: Mon Dec 07, 2020 10:56 pm 
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With a wee search, I located a post on PriceScope from 2004. It is still valid.
Tools you need, a reliable tool for measurement and a scientific calculator.

Angela wrote:
If you know the Pavilion depth, the Crown depth and the Table of a diamond (all given as a % of average diameter), the “all so important “ Pavilion Angle and Crown angle can be calculated easily.


PAVILION ANGLE:
1. Enter the Pavilion depth into your calculator.
2. Divide this by 50.
3. There is a button on many calculators labelled “Tan –1”, or it may be written in small writing above the “Tan” button. Press the “Tan –1” button (or if it is written above the “Tan” button, press the shift button, then the “Tan” button). This is the exact pavilion angle in degrees.

Eg. Pavilion depth = 43.1
43.1/50 = 0.862
“Tan –1” 0.862 = 40.76. This is the exact pavilion angle in degrees


CROWN ANGLE:
1. Divide the Table by 100
2.Subtract this from 1
3. Multiply this by 50
4. Store this figure
5. Divide the Crown depth by the above figure
6. Press the “Tan-1” key. This is the exact crown angle in degrees

Eg. Table = 53 Crown depth=16.2
53/100 = 0.53
1-0.53 = 0.47
50x0.47 = 23.5
16.2/23.5 = 0.68936
“Tan –1” = 34.58. This is the exact crown angle in degrees

I hope this is helpful to forum readers.


Note: This formula only works for round brilliant cut diamonds with no culet (ie pointed). If a culet is present, use the crown angle formula to work out the pavilion angle, plugging in culet rather than table (if you flip a stone upside down, the culet becomes a mini "table").


Also, there is the old style visual determination using only your eyes:
Image


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 Post subject: Re: Microscope Reticle Question
PostPosted: Tue Dec 08, 2020 8:05 pm 
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I find all this provided info very valuable, thank you to all! How about other shapes than RB's?

Can someone shed any light on what this tool is called, I have used for years to measure different lengths of faceted stones. It can be very tedious getting in focus and I find myself not wanting to trust the measurements for calculating a given angle based on the measurements of height of a crown, pavilion, or girdle. The girdle width seems like the most reliable.

Attachment:
GemScope.jpg
GemScope.jpg [ 26.88 KiB | Viewed 612 times ]


Attachment:
GemScope-Gauge.jpg
GemScope-Gauge.jpg [ 35.42 KiB | Viewed 612 times ]


Attachment:
GemScope-Gem.jpg
GemScope-Gem.jpg [ 36.35 KiB | Viewed 612 times ]

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 Post subject: Re: Microscope Reticle Question
PostPosted: Thu Dec 10, 2020 6:30 am 
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The theory behind using a tangent calculation can be used on any stone, not just a round brilliant. The post from Barbara references specific numbers for a RB but if you take the premise (Opposite/Adjacent) then you just need to measure that distance for anything and you could, in theory, get the angle of the facet.

There are some, like step cuts, that you might be better off using the Sin or Cosine because you can get a more accurate measurement of the Hypotenuse and then you would just have one measurement that would be less accurate (either Adjacent or Opposite).

The tool you have a picture of looks almost like someone made it by hand so it could be a custom tool, I have never seen one before and the fact that it looks like the measurements are in inches rather than mm like we use more often today it's probably old enough that I wouldn't have been born when it was used so I can't comment on it much. It looks interesting and would provide a much steadier/accurate reading compared to using a small table gauge.

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 Post subject: Re: Microscope Reticle Question
PostPosted: Thu Dec 10, 2020 6:43 am 
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Angela wrote:
If you know the Pavilion depth, the Crown depth and the Table of a diamond (all given as a % of average diameter), the “all so important “ Pavilion Angle and Crown angle can be calculated easily.


PAVILION ANGLE:
1. Enter the Pavilion depth into your calculator.
2. Divide this by 50.
3. There is a button on many calculators labelled “Tan –1”, or it may be written in small writing above the “Tan” button. Press the “Tan –1” button (or if it is written above the “Tan” button, press the shift button, then the “Tan” button). This is the exact pavilion angle in degrees.

Eg. Pavilion depth = 43.1
43.1/50 = 0.862
“Tan –1” 0.862 = 40.76. This is the exact pavilion angle in degrees


CROWN ANGLE:
1. Divide the Table by 100
2.Subtract this from 1
3. Multiply this by 50
4. Store this figure
5. Divide the Crown depth by the above figure
6. Press the “Tan-1” key. This is the exact crown angle in degrees

Eg. Table = 53 Crown depth=16.2
53/100 = 0.53
1-0.53 = 0.47
50x0.47 = 23.5
16.2/23.5 = 0.68936
“Tan –1” = 34.58. This is the exact crown angle in degrees

I hope this is helpful to forum readers.


Note: This formula only works for round brilliant cut diamonds with no culet (ie pointed). If a culet is present, use the crown angle formula to work out the pavilion angle, plugging in culet rather than table (if you flip a stone upside down, the culet becomes a mini "table").


There's one word in this post I really don't like and it's the word "exact".

Looking at this formula it does make sense, yes. These numbers do however, assume that the diamond has decent symmetry as it is making the assumption that the culet is exactly in the middle of the stone. Similarly it is making the assumption that the table is exactly centered.

In theory it would end up working but as 1bwana1 mentioned, you should be getting the average crown angle rather than just taking a single measurement as the symmetry may be off a little that your eye may not catch it.

That said, if you're looking for at least a rough idea then you could use it as it would only require the normal measurements we would be doing (crown height and table width) rather than having to estimate the measurement from the edge of the table to the edge of the girdle.

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 Post subject: Re: Microscope Reticle Question
PostPosted: Thu Dec 10, 2020 10:05 pm 
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Quote:
There's one word in this post I really don't like and it's the word "exact".

Fair enough.
Original question: Reticle
I have a microscope reticle. Do I use it? Maybe when I first got it a couple of times.
I'd have a hard time finding it now.

What do I do when angles and proportions are required with a mounted stone which was never scanned with a Sarine?
I measure what I can with a Presidium gauge or Table gauge and estimate the rest optically.


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 Post subject: Re: Microscope Reticle Question
PostPosted: Thu Dec 10, 2020 11:19 pm 
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I have a mirau interferometer and epi DIC if you need something more precise. Still need some goniometers though.

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 Post subject: Re: Microscope Reticle Question
PostPosted: Thu Dec 10, 2020 11:37 pm 
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I'm in the market for a "Transporter™" Dematerialization Unit if you have any leads.


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 Post subject: Re: Microscope Reticle Question
PostPosted: Fri Dec 11, 2020 11:02 am 
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Barbra Voltaire, FGG wrote:
I'm in the market for a "Transporter™" Dematerialization Unit if you have any leads.



The one I have is getting rusty from non use since this whole virus crisis started. No traveling at all. In retrospect I should have ordered the optional time travel module when I had the chance.


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