Sunday, September 15, 2013

Breaking an Apatite. Or: How Observation can Interfere with Experiment

So I had the brilliant idea of taking snapshots while my setter, Pierre, set an apatite into my new silver halo ring.  Dark blue sapphire outside, turquoise center, it was going to look fabulous.  Pierre has some very fancy setting equipment.  At his bench there is a huge microscope with very strong lighting that costs several thousand dollars, surrounded by lots of other smaller gadgets.  I guess you need that when you routinely set expensive gems.  Luckily, my apatite had only cost me about $20. 

Ring Inside Ring Holder
First, Pierre carefully clamped my ring into a ring holder, cushioning the outside of the shank with tissue so wouldn’t get marred.  The ring has to sit tight in order for the pressure from setting not to dislodge it.  Then Pierre separated the double prongs.  During casting, prongs that sit close together often have metal in between them, and it is cut apart with a separator disc.  Then the prongs are shaped into claws and the seat is drilled: that’s a little groove on the inside of each prong where the girdle of the gem will rest.  I like my gems set low, and the apatite fit perfectly into the opening.

Separating the Prongs
Unfortunately, the lighting of his microscope was so strong that my iPhone couldn’t cope, so I asked Pierre to lower it.  Which he promptly did, but not without mentioning that he could no longer really see what he was doing.  I should have taken that as a cue.

Having placed the apatite into the ring, Pierre proceeded to push the prongs over the gem with his metal bezel pusher.  

Pushing the Prongs over the Stone
As a final step, he rubber wheeled the prongs.  This means sanding them down with a soft rubber disc so that the places where he marred the metal with the bezel pusher – something which is unavoidable – are filed back out.  Normally this is the tricky step because you don’t want the rubber wheel to scratch the stone. 

Rubber Wheeling the Prongs
As it turned out, in this case, the moment during which the little apatite incurred major damage was minutes earlier.  It happened shortly after the light was turned off in order to accommodate my iPhone.  Ahem.  The third photo shows you approximately when Pierre chipped it. 

Long story short, my apatite didn’t live.  And now there’s a pretty tourmaline in the center of that same ring.  So that’s how it goes.  Apatite is risky business.  With a sapphire, this would probably not have happened.  But from now on, I’m not going to ask Pierre to work in the dark! J

Chip in Girdle on Right Next to Where the Prong Would have Been (Plus Scratches You Can't See)

Friday, September 6, 2013

Working with Cabochons and Rose Cuts

If you are used to working with only faceted stones, you’ll find that cabs and rose cuts are an entirely different animal.  Very little of what you know transfers over to the non-faceted gem world.  Cab pricing and weighs are different, they are judged on a different scale, and most commercial settings don’t work.

First, be aware that cabs and rose cuts are not usually clean gems.  The facet grade rough is – well – faceted, and cabs are the next grade down before rose cuts and then beads.  Cabochon material is therefore rarely as clean as faceted stones.   The quality often ranges from very good (near facet grade) to very poor (totally dead and opaque).  Obviously, I don’t recommend the latter.  Cabs don’t have brilliance either, rather, when set right, they glow, despite inclusions.  Cabs usually rank better in terms of glow than rose cuts because the facets of rose cuts don’t let the gem be as bright.  And of course the term “window” doesn’t apply because to not have window, you need back facets.  Technically, therefore, all cabs and rose cuts have window. 

Spinel Rose Cuts
When you buy cabochons, you can expect a lower per carat price than for faceted stones, but you also need to expect them to weigh more.  On average, cabochons weigh twice as much as faceted stones in the same size.  The exception are rose cuts, because they are flatter and the top facets remove extra weight.  The facets hide flaws, however, so your expectations of a rose cut should be lower than that of a cabochon.  Rose cuts usually weigh about the same as faceted stones.  Often, though, a high quality cab and a low quality faceted stones can come out the same in terms of price.

Finding the right setting for cabochons can be challenging.  Even calibrated stones often do not fit the settings that are fabricated for their size.  Many are too high so that the bezel wall doesn’t fold over right; or they are too low so that the stone vanishes under the bezel wall.  Yet others are slightly too big or too small – the latter applies to rose cuts in particular.  The smaller the cabochon, the more problematic it is if it doesn’t fit right.  So when you choose cabs, watch for high dome and low dome, as the terminology goes.  If you have a bezel already, bring it with you when you buy the stone and see how the stone looks in it. 

Round Commercial Bezels
Add to that, that many cabochons are not calibrated in the first place.  So you have to expect to be making the bezel by hand.  This is even more the case for rose cuts, which are often cut in irregular shapes, just following the natural lines of the material.  The expectation is that for either, you will make your own setting, or have it made. 

When I make bezels for cabs and rose cuts, I usually do a closed back.  I find that many gems look washed out when there is no metal behind them.  The light simply passes through them and that dulls the color.  The exception, for me, is when I channel set cabs for earrings, because then I like the light to pass through.  A ring or a necklace has your skin behind it at all times, and that doesn’t help the stone reflect out.  In earrings, that is not a concern.

Square and Oval Cabochons, Cabochon Bullet