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 Post subject: Faceting Repair work
PostPosted: Wed Jul 18, 2018 7:19 pm 
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Hello all,

I am seeking opinions or suggestions on how best to approach faceting repair work. I have been doing (reluctantly) gemstone repair work for a local jeweler. I say reluctantly because of the liabilities but its more of a favor and he is a fairly high end and award winning jeweler. Typically it is to re-polish the table and crown on abraded or damaged sapphires. Generally the overall size meaning (girdle perimeter) needs to be unchanged. These stones are from his clients rings in which he usually creates a new design. Of course these stones are originally cut overseas and do not possess any precise angles or perfect placement of the facets. Many times the stones are heavily abraded and pitted.

My process has been to painstakingly try to locate each facet and record the angle, index, and cheater position for each facet. There is no perfect symmetry so every facet has a unique index and angle. Then using a prepolish zinc lap essentially cut (re-skin) the facet and try to clean up the abrasion and have reasonably good meets. I'm not looking for perfection because I would have cut away too much material. Depending on the stone and girdle thickness they usually come out at least 90% clean and look better than they probably ever did with very minimal weight loss. And to date everyone has been pleased with the result. As you can imagine, this is a very slow process and I feel I can't charge enough for my time. It would probably be much faster to ignore the original facet pattern and cut in new facets at a slightly steeper angle and arrange them perfectly and possibly create a different design. I have been reluctant to do just that because I'm not involve in the front end of the sale and this seems like a safer approach in case of errors.

I am curious how others tackle this kind of job and how they charge. Any opinions and suggestions is appreciated. I've attached a recent job. It was particularly heavily abraded.

David T


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 Post subject: Re: Faceting Repair work
PostPosted: Thu Jul 19, 2018 3:09 am 
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Location: Cape Town, South Africa
I have done lots of similar repair of sapphires, recutting the whole crown by eye. My clients know there will be minor weight loss, but as the aim is revived appearance none of them object. It is important to know if the stone is going into the original setting or a new one. If the former, the original girdle must be retained. If the latter, knife-edge girdles can be ground (and polished) a little thicker to provide some wiggle room. For recutting the crown I use a dual lap (a Gearloose Redwing but any similar dual lap will do) with an outer band using anything from 3000 to 8000 mesh diamond paste, and the inner band with 100 000 mesh diamond polish. This allows one to recut and polish each facet without changing settings. First I recut and polish the table, dropping it enough to allow future star facets to remove any residual damage around the edges. Then I recut the main facets at angles slightly below the original, but avoiding cutting into the girdle, leaving a suitable table width and removing any damage between the mains meets themselves. Initially I just guess the angle, touch the stone to the lap, look with a loupe to see where it is starting to cut, and adjust accordingly. Each facet is polished on the inner band immediately after it is cut, with no need to record anything. Then the star facets are cut in and polished to meet neatly around the table and reach about a third of the way to the table. Finally, the break facets are placed by trial and error, again an initial touch on the outer band of the lap tells you which way to adjust angle and cheater to get the breaks to meet the stars. Sometimes there is a little residual damage at the girdle because you don't want to intrude on the girdle. If the original girdle is thick, as they often are, then this is not an issue and you can get all the meets to meet nicely. The dual lap makes the process quick - should not take more than an hour or two.


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 Post subject: Re: Faceting Repair work
PostPosted: Thu Jul 19, 2018 6:14 am 
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Thanks Duncan,

I'm impressed. I don't know how you can do it in a couple hours. I confess I don't do this everyday. Your description is pretty much how I've been going about it. I do take the setting in consideration. I am currently using a DiaZ+ dual lap. If the stone is heavily abraded, one problem when jumping to polish is that the pits harbor contaminate from cutting on the zinc portion. I have to make sure it is pretty clean. I may be somewhat overly cautious when initially lining up each facet and I have to use the cheater extensively. I record everything so that I can go back if needed. I'm thinking I should probably use a 120 index gear instead of a 96 to give myself less reliance on the cheater. So I see how I can cut some time (pun intended). The stone in my pics is a little over 4 cts. What is a reasonable average price for that type of repair?

Thanks again for your for your input,

David T


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 Post subject: Re: Faceting Repair work
PostPosted: Thu Jul 19, 2018 7:52 am 
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Hello David
I do clean the stone (with alcohol because I am using up my stash of oil-based Diastiks) before polishing each facet. The only one that ever gives trouble is the table, because of junk in the remaining abrasions around its edges. You can recut the star facets first to avoid this, but that adds to the time because you probably have to come back to them later to make them meet. With experience I have become quite good at guessing the angle and index setting needed to start recutting a facet. On really irregular stones I don't necessarily even try to follow the original facet placements, just recut to make a more symmetrical crown. With most of these stones the bulk is in the pavilion, some have very low crowns to start with, so whatever you take off the crown is going to have only a minimal effect on the finished weight. If it's a really special stone with an initial carat weight just above a whole number, then you have to be more careful. Not recording facet settings saves time, although sometimes this comes back to bite you if you have to tweak something, like removing a residual chip at the edge of a main facet that the recut stars and breaks did not cover. I have learned to temper my perfectionism when doing these recuts. The improvement is so dramatic that nobody notices a slightly over-cut meet. Cost? I am in South Africa where the cost of living is still considerably lower than in the USA or Canada. You may laugh at what I charge, but then I don't depend on faceting for a living. A sapphire crown recut works out at around US$75-100, depending on how long it takes. There are commercial cutters in Cape Town who do it for less than half that, but their finish is not as good.
Duncan


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 Post subject: Re: Faceting Repair work
PostPosted: Fri Jul 20, 2018 6:49 am 
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Many thanks again Duncan,

I imagine if I did this more and steady I would get quicker. Fortunately I don't depend on this for a living either and I rather cut a new stone or work on a setting of my own. I'm charging about twice that depending on the PIA factor. So far everyone is pretty happy and they keep coming back to me so I guess all is ok.

I think my biggest fear is if something goes horribly wrong, through no fault, some of these stones are crazy expensive. I have a disclaimer that it is a possibility that the stone can crack or explode or whatever under the stresses but no one wants to think about that. Another reason why I limit how much I want to get involved in repair work.

If anyone else wants to offer an opinion I'm all ears.

David T


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