New Article by Jim Rentfrow - Gemstone Cutting, Step by Step

Hi Jim,

Your article is a very nice informative pictorial illustrating the fine gem cutting process in detail. Well done!

A thanks has to go out to Pricescope too for featuring this article, it shows genuine support as a consumer advocate web site by making this information easily accessible to Pricescope members, and colored stone enthusiasts in particular. I'm very happy to see this here. I look forward to future features.

Regards!

Jeffrey Hunt

Very cool!

-A

Written by Jeffrey:Hi Jim,

Your article is a very nice informative pictorial illustrating the fine gem cutting process in detail. Well done!

A thanks has to go out to Pricescope too for featuring this article, it shows genuine support as a consumer advocate web site by making this information easily accessible to Pricescope members, and colored stone enthusiasts in particular. I'm very happy to see this here. I look forward to future features.

Regards!

Jeffrey Hunt

Appreciate the comments Jeffrey-thank you. We've just added the new CS section to our journal, and we welcome articles from colored stone industry professionals. PS is evolving, and it is exciting to see consumers and trade members bring color to the table. Thanks to all of our CS participants-who make this forum so lively and informative.

What a great article. Thanks Jim for taking the time to put it all together.

Great end photo Jeff, as always

Question about polishing the girdle, why do you do it at the end of polishing the crown instead of after finish polishing both the crown and pavilion?

Thanks for all the comments everyone.

Stone Cold - I polish the girdle before I transfer the stone to complete the pavillion. The reason I do this is because I know my angles are at 90 degrees and sometimes, during transfer, a stone may move and get out of alignment. This can cause the polishing to take longer or adjustments to be made to get the stone back into alignment. Polishing the girdle at this stage is also less risky of causing any chips or other damage to the stone then at the end of the process. If any damage does occur the stone can be quickly recut or repolished to remove the damage. I hope that helped answer your questions, let me know if you have any others.

Thanks. I ask because from what I seen on diamond cutting the girdle is polished last, differences due to the hardness of the material?

Another question is how do you set the facet angles?

Angles are set by moving the mast of the faceting machine up and down. The higher the mast the steeper the angle and the lower the mast level the lower the level and angle used for faceting. I included some photos of the mast below and a link to a photo album showing some of the tools used in faceting.

Diamond cutting and colored gemstone cutting are very different. However there are faceters who do polish the girdle last on a colored gemstone. I have done this in the past if the girdle had to be touched up prior to taking it off the dop stick or when I had to walk away from my machine and forgot to polish it before I transferred the stone.

Attachments

This is the MDR faceting machine I use. The mast is on the right side of the machine

Machine.JPG (227.25 KiB) Viewed 1092 times

This is the angle dial that shows what angle the machine is set to.

Angle Dial.jpg (206.79 KiB) Viewed 1092 times

This is the index gear of the machine, for setting the facet pattern on the gemstone

Index gear.jpg (168.99 KiB) Viewed 1092 times

Stone Cold - if that link is not allowed please remove it from my post. It is to a non selling photo album with pictures of the tools used for cutting.

JIm,

Thank-you for your informative article much appreciated.

Is it common for most faceters of diamond or colored gems to cut the table first?
I've been working with the centre angle method of facet design and the table is cut last in this method.

When would you use one or the other?

With colored gemstone cutting there is a preference for cutting the pavilion first among precision faceters. However, there are some of us who often cut the crown first because we prefer that method or that is how we were taught.

The reason I cut the crown first is that this method is the way I was taught and I can manipulate the pavilion design once the stone is transferred. Another reason is that if I cut the crown first and I have a lot of material on the pavilion that will get wasted I can adjust the angles quickly in gemcad.

If the performance will not be affected much by doing this then I will often adjust the patterns or angles. This has also let develop many interesting facet patterns that I start to cut regularly afterwards because I liked the look of the stone.

Diamonds are cut a little differently but I believe, after sawing, the saw plane of the diamond becomes the table and is cut first. After this step the diamond has the 8 main crown and pavilion facets placed. The American Institute of Diamond Cutting has an interesting page with photos documenting the diamond cutting process from start to finish that you can view.

Thanks for the images, Jim and also for the heads up to the diamond cutting page.

Jim, I cut about the opposite way you do. I don't do much preforming, and cut the pavilion first. This way I know I'll have the depth needed to finish the stone, and if there is a depth issue, I'd rather make the adjustment in the crown than the pavilion, since the crown angles are less critical in most designs to the overall performance of the stone.

Many designs require the pavilion facets to create the outline of the girdle, I'd think you would need these before you would get to the crown. What's your typical yield? Do you think you are saving material cutting the crowns first?

thank you, that was greatly informative for beginners of collecting like me.

I have a related question: What kind of charges are incurred in getting a crystal cut? I am sure it depends on gem type, size, etc etc. I have a peridot crystal, about 40 carat in weight. So I am looking for information about pricing related to that.

Thanks...

Hi Gene,

My typical yield is around 35-40% on most designs. You can use the crown facets to create the outline of the gemstone the same way that the pavilion facets are used to create the girdle. I have done this in the past with various designs and it has worked well. I pre-form first, cut the table, and then follow with the main crown facets. The facets can be lined up perfectly by going back and making minor adjustments on the girdle or using the "cheater".

When I have cut gems using the pavilion first method in the past I didn’t like the way they turned out. The process didn’t work as well for me as cutting the crown first; probably because I am used to completing the crown first on my gems. I could be saving rough by cutting the crown first, but the truth is, this is the way I was taught to cut and the results turn out very well. So I keep doing it that way even though its the opposite of most other faceter’s today.

vanterminator,

Charges vary from faceter to faceter. Some faceter's will cut other peoples rough and some will not. I have seen charges based on an hourly rate, a per stone rate, and a finished carat weight so I would check around and get quotes. I am assuming for a stone that size the prices could be from $250 to $500 dollars because of the size and the amount of time it would take to get cut.

Hopefully that helps.

thank you very much for the informative response. I will probably send out requests for quotes from some people when i have a little more free time to devote.
thanks!

I just noticed this sticky.

Thanks for sharing, Jim! Your article is so interesting, I loved being able to look at all the pictures.

What a fascinating and informative article - thank so much for writing it up and posting, Jim! I am also enjoying the discussions in this thread

Very Neat Jim;

I am sure it helps many that have not cut to see the machine; the quill, angles, degrees, etc. I know it would have helped me with the concept if I had not cut a gem.

Great learning tool...

I am the old school like Gene and i cut the pavilion first; but I have been doing it so long and have been a member of the old school guilds that taught the crown first and I have a ton of old diagrams that list cutting the crown and table first; so I do not think it is a right or wrong thing; just what you get use to doing and if it works; well keep doing it

Thank you for taking your time to share this informative post with us all. " A picture is worth a thousand words" ...

Happy New Year !!!!!!!

Most respectfully;

Dana M. Reynolds, csmg
ASG # 96CGE42

. Great job, Mr. Renfrow. A lot of work went into this presentation (you too, Erika, aka 'Coati Mundi').
. The mast-type machine shown is not what diamond-cutters use. There are other types of faceting machines, I avoid anything with a mast since rigidity is important to repeatability when cutting a row of similar facets, as on a round brilliant.
. Pic below is of my 3rd and preferred machine - the Raytech-Shaw faceter, similar to Imahashi and the machines diamond cutters now use. It is a tripod handpiece which sits on a platform (lower right) that is raised or lowered to control depth of cut. You can lift the handpiece and turn it over to inspect progress. I make tiny corrections by putting a 3x5 filing card under one foot. Diamond cutters call the handpiece a 'tang'.
. In Burma my son saw them cutting rubies and sapphires using 'handpieces' of similar tripod concept, except they were tree branches that went over their shoulder and the two feet rested on a shelf behind them. It was so long that the arc was insignificant and they controlled depth of cut just by raising or lowering the end with the stone. The dop was a nail, indexed by eye and held tightly in the slot by a wingnut. Four cutters used the same lap at the same time. Who can compete financially with that, and who will pay the difference for a better-cut stone?

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Faceter1.jpg (67.39 KiB) Viewed 527 times

. And here is the machine used by my friend, Anton Vasiliev, in Moscow. He cuts only colored stones and had a profitable business doing so.

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G2.jpg (134.08 KiB) Viewed 526 times

Wow! What a great article! I will most definitely refer my clients to this. Are there thresholds to the kind of tools you use for gem cutting in relation to the hardness of gems? I know for diamonds they are cut against each other. Are there are other gems that are cut this way?