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 Post subject: Re: Re:
PostPosted: Mon May 21, 2018 7:46 am 
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I have been trying to follow flameswithin's cutting instruction of 2010 for a 'native cut' oval, below, without success. Without changing the angles within a tier as one goes from the wider to the narrower end of the stone, the second tier facets become very irregular, and the ones at index 21... impossible to cut. Am I missing something here, or is there something fundamentally wrong with these instructions?
flameswithin wrote:
Anyway, RocketGems, if I've read your question right, I feel like I've been searching for the same thing for a few years now. I have a lot of respect for what native cutters can do, and what they probably *could* do if they weren't being paid pennies per stone. The reality is that you CAN cut "native"-looking stones with proper angles and get good results. Don't listen to the nay-sayers! heheh. To prove my point, here are a few ovals I've cut with portuguese style pavilions.
Image Image Image Image

An important note--the culets of these ovals don't meet in a point, they meet in a keel. Dunno if that matters to you or not. I also don't cut them meetpoint--I grind an oval preform first, mark a line for the girdle and cut my pavilion facets to the line. I don't have a gemcad file to offer you, but here's what I do in Quartz, for an example.

I know I want the culet tier to be 43 degrees. I've found that 2 degree increments makes a nice transition, so I'll cut my first tier at 47 degrees all the way around, at indicies: 96, 5, 10, 14, 24...
Second tier at 45 degrees, indicies: 3, 7, 12, 21...
Third tier at 43 degrees, indicies: 96, 5, 10, 14, 24...
(Note-- You can actually use normal SRB indices [96, 6, 12, 18...], but you'll find that your facets around 96 will be huge and those around 24 will be tiny)

Then for the crown, just find any oval crown you like, make sure the L/W matches your preform (scale it in gemcad if you need to), and cut it in. This works for me every time with perfect meetpoints. As an alternative, if you really want a culet that meets in a point, open an SRB in gemcad, give it a 3-tiered portuguese pavilion, then stretch the L/W into an oval. Boom. There you go.

I've tried cutting two ovals so far with step cut pavilions and I haven't liked the results. Dunno, just seems like the light bounces everywhere but where you want it to, heh.

Throw off your meetpoint shackles, comrades! You can cut native style cuts without sacrificing quality!!!


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Mon May 21, 2018 9:40 am 
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I often cut in this style. In fact I almost never cut from a diagram. I let the stone dictate the shape, the angles and the pattern. In my opinion, this is the best way to maximize the yield, while dealing with issues of color, and clarity in the rough.My normal yields end up around 40%, and it is not uncommon to exceed 50%. I teach this system here to students at the San Diego Gem and Mineral Society one day a week.

For an oval I usually follow the 2, 4 6, 8, makes an oval look great poem. Meaning you cut the indexes off the prime indexes (0/96) as follows.

1st index +- 2 =2
2nd Index +- 2 +4 =6
3rd index +- 6 +6 = 12
4th index +- 12 + 8 = 20

Giving and index value of 2, 6, 12, 20.

The entire shape of a stone can be described by knowing the indexes of the first quarter of the stone assuming a 4 fold symmetry like an oval. This system allows you to cut any of the normal shapes of stones by eye without diagrams. After all, in order to describe the cut of a stone you only need to know the indexes of the first order of symmetry, which is most often only 4 numbers. You will learn to have perfect meet points, and no windows, but get all the advantages of native style cutting.

The key is understanding that facet size and shape is controlled by relative width, and the difference in angle between rows of facets, not the absolute angles. The facet width will be controlled by the depth you cut each index as you shape the girdle. To control the height of a triangular, diamond, or kite shaped facet the smaller the difference between two rows the taller, the greater the difference, the shorter the facet will be. So, in order to match the height of the facets around the oval (or any other shape), you must change the difference of angle between the rows.

I know this description is unclear. It is a complicated concept. I would be happy to try and teach it in a step by step way. The best way is not to jump straight into an oval, but to learn the facet shaping technique on a round first.

Steve


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Mon May 21, 2018 12:52 pm 
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Hello Steve

Thank you for your reply. Your description is not unclear. You have tried to answer this question for me before, but evidently I haven't got the hang of it yet. If I understand correctly it confirms that you need to change the angle for successive diamond-shaped facets as you cut around an oval towards the narrower end. I can cut a conventional brilliant oval on the fly, but with diamond-shaped facet 'native cuts' I struggle to know which intermediate index settings to use and to guess by how much to change the angles to get uniform tiers.

Do you use the same fundamental index settings 2, 6, 12, 20 for ovals of any proportion, or do you vary these systematically?

Duncan


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Mon May 21, 2018 2:15 pm 
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Duncan Miller wrote:
Hello Steve

Thank you for your reply. Your description is not unclear. You have tried to answer this question for me before, but evidently I haven't got the hang of it yet. If I understand correctly it confirms that you need to change the angle for successive diamond-shaped facets as you cut around an oval towards the narrower end. I can cut a conventional brilliant oval on the fly, but with diamond-shaped facet 'native cuts' I struggle to know which intermediate index settings to use and to guess by how much to change the angles to get uniform tiers.

Do you use the same fundamental index settings 2, 6, 12, 20 for ovals of any proportion, or do you vary these systematically?

Duncan


Hi Duncan,
Yes, you need to change the angle as you go around the oval. By choosing the width of cut at each index you can make the 2, 6, 12, 20 indexes work for the vast majority of L/W proportions with ovals. This index set also has an exact middle index to cut the alternating rows which takes care of your next issue.

The examples below only list the first quadrant of the oval. I like to cut in pairs or quads making sure not to change mast height when cutting sets. You do change for different sets make the outline. Ths results in perfect symmetry for any L/W ratio.

First: Cut the side set which is +-2 off the 0/96 index and the 48 index. This gives you the center of the oval with each side matching.

Second: Cut the end set. These are the +- 20 Indexes. Easier to see as +- 4 from the 24 and 72 indexes. You will now have your L/W defined.

Third: Cut the corner set. The +- 12 Indexes. Make this set of facets just a little wider than the end facets. Watch as the end facets narrow as you cut these.

Fourth: Cut the intermediate side facets at +-6 Indexes. Watch both the side and corner facets and cut to a depth that sizes the facet the way you want.

At this point you should have a perfectly symmetrical oval with a L/W ratio of you choice.

Now to cut the pavilion. You will cut your rows with one of two index sets. The first row (A) will match the indexes of your girdle outline. The second row will have indexes 1/2 way between, (B row). You will alternate A/B rows to cut the culet

Row A: 2,6,12,20 Row B: 0,4,9,16, 24

So let's say that based on the width/depth ratio of the stone you decide to start your first row at 52 degrees. You will use the A row indexes to cut a straight girdle line around the stone. We know we will deed different angles at the corners and ends in order the get the height of the facets to match. Since the corner and end facets are usually narrower that the sides, the difference in angle between the rows will need to be greater at the ends than the center. To keep it simple we will onl estimate here. We will cut the corners 1/2 degree, and the ends 1 degree less steep than the sides.

Example first A row
+- 2 at 52 degrees
+-6 at 52 degrees
+- 12 at 52.5 degrees
+-20 at 53 degrees

Now we need to cut the second row on the B indexes. I find that a pleasing shape results from a difference of 2.5 to 4 degrees difference between the first two rows. So let's choose 3 degrees for the example.

Example second row

+-0 at 49 degrees
+- 4 will be very close to 49 degrees. Just vary enough to make it match the 0 in height.
+-9 adjust the angle to make heights match
+-16 adjust the angle to make heights match
+-24 adjust the angle to make heights match

You should now have a row of triangles of the same height all the way around the stone.

The third row will be cut on the A indexes. Choose an angle that gives you a pleasing shape for the diamond shape that you are creating, and that will lead to closing the culet before you cut enough rows to be below the critical angle of the material you are cutting.


Remember ar you cut more rows the stone will be getting narrower. Finally it will get to the point that it pinches out the facets toward the ends of the stone. This is good, just stop cutting them when they get too small to make sense. The final rows will normally only consist of the first two indexes of whichever row type (A/B) you are cutting.


These indexes also work out perfectly for the crown either as standard brilliant crown as follows. Or as a Portuguese style crown using the same A/B indexes as the pavilion.

Row 1 (Girdle facets) 2,6,12, 20

Row 2 (Mains) 0,9,24

Row 3 (Stars) These will vary based on the L/W of the stone, the width you made each of the index facets that describe the shape, and the height you choose for the mains. We will discuss how this works when you get to cutting the crown.

Hang in there and we will work through this. Once you get the concepts you will be off and running on most shapes you commonly see stones.

Steve


Last edited by 1bwana1 on Mon May 21, 2018 10:11 pm, edited 1 time in total.

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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Mon May 21, 2018 2:48 pm 
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Steve, thank you for your patient, detailed guidelines. I will tackle this again tomorrow. Duncan

Tomorrow has happened. The San Diego Gem and Mineral Society members are fortunate in having you as a teacher. Your detailed instructions have made me feel rather sheepish that I couldn't figure it out for myself. But after three attempts on a long-suffering marble I have managed to cut a more-or-less successful 12x14 mm oval pavilion. Getting the facets in each tier level seems to be key. With your original angle suggestions it went like this:
2, 6, 12, 20 (52*, 52*, 52.5*, 53*)
0, 4, 9, 16, 24 (49*, 49*, 48*, 46*, 45*)
2, 6, 12, 20 (46.5*, 46*, 44*, 41.5*)
0, 4 (43*, 43*)
The last two sets of facets on the third tier (12, 20) were the most tricky to place. It think the 41.5* was necessary because the end facets (24, 72) were rather broad on this fat oval. I am not going to post a picture because it's only a pavilion on a marble, the facets are not polished, and right at the end the culet chipped. This is all practice, and I'll mutilate a few more marbles before I try to do this on a proper gemstone.

I have one more question. You wrote "So let's say that based on the width/depth ratio of the stone you decide to start your first row at 52 degrees." This is a fairly important starting point. How is this initial angle determined by the width/depth ratio? It is easier to ask you than to experiment, but what happens if you start at 55 degrees and use 5 degree initial steps? To get good recovery, presumably you aim for 'fat' stones, but without the culet facets below the critical angle.

Once again, thank you for your generous help.

Duncan


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Wed May 23, 2018 10:10 am 
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Another day, another marble. I ran into the same problem as before with the third tier facets on the corners. The 12s cut in at 43.78 degrees, and the 20s at 43 degrees but these were long and very narrow, leaving the second tier 24 & 72 facets (at 45 degrees) too long and broad. Steve, I don't know if you can diagnose the problem from my description, but I suspect my corner and end facets (12s and 20s) are too broad using the 2, 6, 12, 20 index formula and equal width girdle facets. I have to take a break from this now, but may get back to faceting over the weekend and will try with a higher length/width ratio.


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Wed May 23, 2018 12:57 pm 
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I just recently started cutting in the way that Steve has described and I really love it. It feels free and I feel like my skillset has definitely been sharpened by learning to cut like this. I used to dread ovals but I now I think they're really fun.

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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Wed May 23, 2018 4:39 pm 
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Perhaps you can make a video of this kind of cutting? I have a feeling with a video the description would be easier to follow.


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Wed May 23, 2018 10:36 pm 
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Duncan,
Remember that an oval is just a round with the sides stretched, and the corners pinched. So the side facets should end up larger than the end facets. Also you control the height of the facets by the difference in angle between rows.

Keep in ing the the angles in my example we just made up for the explanation. They will need to be adjusted to cut a real stone.

The starting angle is chosen to retain the weight of the stone, produce pleasing shaped facets, and to close the pavilion before you violate the critical angle of the material. What you need to pay attention to is the depth of the stone in proportion to the width of the stone. The length does not usually come in to play as the keep of the culet will just grow with the length automagically (LOL). A stone that has a depth of around 60% will have starting angles in the mid 40's and just a few rows. A stone with D/W around 70% will start in the low 50% and have more rows. Once the depth goes above 80% I usually use a technique I have developed to make a false girdle.

Sounds like you are making good progress.


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Wed May 23, 2018 10:47 pm 
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justinkprim wrote:
I just recently started cutting in the way that Steve has described and I really love it. It feels free and I feel like my skillset has definitely been sharpened by learning to cut like this. I used to dread ovals but I now I think they're really fun.



That is great Justin. Learning to cut like this will make you a professional, and you will be more competitive in the market. Think about this, if you are able to cut attractive, desirable stones and get high yields you can compete for good rough better. If you get 10% better yields and can offer just a couple of percent more for the best rough, you will have top stones, and a lower per carat cost than the typical meet point faceter. I often hear meet point faceters complaining about not getting shown great rough in expensive species. I am sure that being in BK you are finding that good rough is in the market. You just can't be competitive with yields in the 20% range. Things that make say Hummmmm.....

Sound like you are starting to become a "gemstone cutter" instead of a faceter. There is a difference.

I have started developing methods, materials, and tools to teach gem cutting. I have some ideas that I think would be innovative and useful. Given your interests and energy we should talk and share ideas. Will you be at the AGTA show in Vegas at the end of the Month?

Steve


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Thu May 24, 2018 11:59 am 
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This afternoon I found time to have another attempt at cutting an oval pavilion. This one went better; with a 1.377 L/W ratio, narrower end facets, and the 1st tier corner and end facets at higher angles. The 2nd tier facets placed nicely with neat corners and the culet finished off at 43 degrees. So I've got the hang of it - at least this once. The 1st tier facet angles, depending on both pavilion depth and L/W ratio, seem to determine the success or failure of the higher tiers. I suppose it takes experimentation with various L/W ratios, girdle facet relative sizes, and pavilion depths to get a feel for what 1st tier angles and subsequent increments are appropriate.
It has been an interesting learning experience. I started faceting before the advent of meetpoint technique and taught myself laboriously how to cut oval brilliants. The meetpoint oval designs of Long & Steele were a liberating revelation for cutting standard proportions and designs repeatedly with precision. The present exercise means unlearning some of the reassuring aspects of meetpoint faceting. It's a bit of a challenge, managing the variables. Steve, once again, thanks for your guidence.


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Thu May 24, 2018 12:26 pm 
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Sounds like we are making great progress Duncan. Congratulation! =D>

Now turn that marble over and let's do the crown.


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Fri May 25, 2018 9:34 pm 
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After going through this thread I'm surprised there isn't any mention of parallel bar pavilions, as unlike the tradition style they aren't reliant on starting at the girdle to produce this effect.

https://www.gemrockauctions.com/auction ... d62-463870
This demantoid garnet uses it and I have seen it done on rectangular sapphires elsewhere. Words are better with pictures so here's a reproduction of this technique in GemCutStudio:
Image
Each tier of facets is cut at 2 indices difference to the other, with the mains cut at 12-16-32-36 and such.
With enough tiers the technique ends up producing a lot of small triangle-shaped reflections that have a resemblance to commercial cuts with a 4-facet culet.
Render in Topaz


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Sat May 26, 2018 4:23 am 
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Hello Shifter55
The render in topaz looks very nice. Would you mind providing the angles you used? I can't get the facets quite parallel in GemCad.
Duncan


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 Post subject: Re: Where are the high-end traditional faceting designs?
PostPosted: Sat May 26, 2018 6:54 am 
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Duncan Miller wrote:
Hello Shifter55
The render in topaz looks very nice. Would you mind providing the angles you used? I can't get the facets quite parallel in GemCad.
Duncan

Here's the design itself with some changes to make it meetpoint.
As for doing it on GemCAD... you need to select both ends of the diagonal edge of a tier, and then type in a new index to get a parallel facet. Just delete the old coordinates and you can place it wherever you want. To get the equal mast height you need to copy the Center-to-Facet distance or work your way inwards from the steepest set of facets.

I actually forgot that CtF Distance function lets you do this, makes sense given it's the same sort of thing as ECED?


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