In a quandry - is a tilt window common in RB and Portuguese cuts?

[cellentani]

I have gotten two round-cut gemstones: a round brilliant awhile ago, and just recently, a round Portuguese cut - both of them tourmalines. What is baffling to me, is that they both have windows when tilted, even though I have every reason to believe both cuts were well-executed. I have an aqua asscher ring that has a huge tilt window, but I just assumed it was the quality or type of cut. My diamond is a round brilliant, and no matter how severe the tilt, it shows no window - absolutely none!

I feel like I have to view these gemstones straight-on in order to avoid the window, and this directionality drives me crazy. Is this normal for round cuts, or am I being way too picky? And why doesn''t my diamond have a tilt window, when a RB gemstone does?

 

[chrono]

It is explained here:
https://www.pricescope.com/community/threads/window-when-stone-is-tilted.109957/

A lot of it has to do with the Reflective Index (the higher it is, the less of a window tilt) and cutting. A diamond has very high RI plus precision cutting so you will almost never see a window tilt. Seeing a window tilt is fairly common in gemstones and if well cut with high RI (garnets, spinels and a few others), you will probably not see it as often.

 

[Barrett]

Diamonds are usually the best cut and most of the time you cannot see through a diamond from the back since all the light is reflected back out through the table. Colored stones rarely are cut as well diamonds and they have much lower refractives indices so have to be cut much differently. Most cutters of colored stones try to get the color in the bottom of the pavilion so it will reflect evenly throughout the stone. The concntration of color on the girdle is because it is the thickest part of the stone usually. Paler color is usualy due to the color zoning in the crystal and sometimes the cut can help but not always. Anyways the window in colored stones has nothing to do with color but mainly with the cut.

 

[cellentani]

Thank you, thank you Chrono and amethystguy - I think you just saved me from returning a nice stone. And Chrono, that link was particularly helpful.

 

[tsavvy]

The explanations and link were very helpful

I''m glad that you were also rescued from returning a great stone, Cellentani. Any pictures to share?

 

[cellentani]

Date: 6/12/2009 5:25:48 PM
Author: tsavvy
The explanations and link were very helpful

I''m glad that you were also rescued from returning a great stone, Cellentani. Any pictures to share?

I just snapped a quick few. These don''t show accurate color at all, but you can see the facet pattern of the portuguese cut really well.

 

[cellentani]

Showing the tilty-window-thing.

 

[cellentani]

I know this isn''t a real window, but it bothered me at first that I couldn''t see all the facets.

 

[cellentani]

Again, the color isn''t true in any of these - my hand is making everything more peachy.

 

[cellentani]

forgot the pic:

 

[cellentani]

Last one. I''ll try to get photos that show better color later.

 

[T L]

THe table is kind of large, which would be accounting for the larger than usual tilt window. I have a precision faceted tourmaline RBC with extra facets on the pavillion, and a much smaller table. This stone, even though it is low RI, has a very minimal tilt window. Setting it also helps. If you love the color, then keep it. If you don't like the color or the cutting, then return it.

 

[icekid]

Date: 6/12/2009 6:34:50 PM
Author: tourmaline_lover
THe table is kind of large, which would be accounting for the larger than usual tilt window.

I was wondering if this might be part of the reason, as well. Again, setting should help. pretty stones, though.

 

[chrono]

I agree with TL and Ice. The window tilt is normal but maybe it is more easily visible than it could be, especially for a portugese cut stone, which TL attributed to a larger than expected table.

 

[PrecisionGem]

I''m not a big fan of a Portuguese round. Especially in a smaller stone, the cut always has a lot of extinction, as you can see in your first picture.
Stones with large tables, are prone to a tilt window pretty quickly. Checker cut crowns, and higher crowns with small tables will help avoid this. The material is a big player. The refractive index is a measure of how the stone bends light. Gems like quartz, opal, sunstone etc, have pretty low RI around 1.54, where a diamond or cubic zirconia are very high over 2. You almost can''t go wrong cutting one of these high RI stones.

 

[T L]

The only gems I like large tables on are diamonds. It helps to give them more dispersion, and they face up larger. However, large tables on stones are not my cup of tea. I prefer higher crowns and smaller tables, as Gene noted. They help to reduce tilt windows on low RI gems. Of course, who am I to talk with all my bad native cut gems

I actually have a precision faceted dark rhodolite garnet. It has an antique cut, and the table is very very small. As a result, it sparkles like crazy, even though it is a very dark stone. Even in dim lighting, the stone has life.

 

[T L]

Found a picture on the net of a high crown and small table faceted light blue topaz. I think this kind of gives you an idea of what I''m talking about.

This stone is as low RI as you can get, and the color isn''t really the greatest, but

, there is no way that this stone could be better cut. The cutting accounts for the lack of color by giving it depth, and the table is small, and the crown high, so the tilt window is very diminished, and it looks like it has the sparkle factor of a higher RI gem. I''m so impressed with the cutting on this stone.

 

[cellentani]

Thanks for the pics TL - I love that blue topaz! My morganite has a high, almost domed crown. It does have a tilt window sometimes, but it just doesn''t bother me, and I can''t figure out why.

 

[T L]

A low RI stone will ALWAYS have a tilt window, but with specialty cuts like the one above, they''re not as bad. With a large table, the tilt window is much larger. In fact, when I am shopping for a precision cut gem, I do take note of the table size in the picture. I prefer when stones are shown at a tilt to easily see this, but if you see one face up at you, take note of the table in relative proportion to the rest of the stone. I think one of the reasons that everyone is so enamoured with Barry''s rounds is because he does proportion the table accordingly, and he seems to cut lower RI stones with a smaller table.

 

[LD]

I have a sneaky feeling that both tilt windows will be dramatically minimised when the gems are set (if you decide to keep them). Do you have an empty setting you can pop them in to see?

 

[cellentani]

Date: 6/13/2009 12:04:31 PM
Author: LovingDiamonds
I have a sneaky feeling that both tilt windows will be dramatically minimised when the gems are set (if you decide to keep them). Do you have an empty setting you can pop them in to see?

Let me go wash the Cheetos off my hands and find out...my empty settings aren''t very nice, though.

 

[cellentani]

Here''s one:

 

[cellentani]

Another. Doesn''t look as bad....

 

[cellentani]

I like how this looks, though.

 

[cellentani]

and this one too.

 

[cellentani]

more window.

 

[tsavvy]

It looks like the tilt windowing will remain visible in the setting, but the cut does look really neat straight on. I really like the gem on the right - the color and cut both look great.

 

[cellentani]

Date: 6/13/2009 3:09:58 PM
Author: tsavvy
It looks like the tilt windowing will remain visible in the setting, but the cut does look really neat straight on. I really like the gem on the right - the color and cut both look great.

Me too. That''s my first gem from Gene, and my first umbalite.

 

[chrono]

Date: 6/12/2009 10:37:03 PM
Author: tourmaline_lover
The only gems I like large tables on are diamonds. It helps to give them more dispersion, and they face up larger. However, large tables on stones are not my cup of tea. I prefer higher crowns and smaller tables, as Gene noted. They help to reduce tilt windows on low RI gems. Of course, who am I to talk with all my bad native cut gems

I actually have a precision faceted dark rhodolite garnet. It has an antique cut, and the table is very very small. As a result, it sparkles like crazy, even though it is a very dark stone. Even in dim lighting, the stone has life.

TL,
For diamonds, I actually like high crowns and small tables too; it gives them much better coloured light return aka FIRE! It does seem to help light coloured gemstones too. I''ve seen this in a deep red spinel which gave good red flash but the extra depth made the stone too dark. The cutter tried to hit the 2 ct mark and so a lot of the weight was in the crown.

 

[chrono]

Cellentani,
Wow, it doesn''t take much to see that window tilt, even when on the hand. Is this still within the return period? Are you all right with what you are seeing?