What typs of gems don't have much of a tilt window?

[cookies]

Besides diamonds, what types of gems usually don't have an obvious tilt window?

The faceted gems I have seen so far in real life, including aqua, sapphire, amethyst, and zircon, all have a tilt window to some degree. That is, when I tilt the gem, I always see a dark hole..

Do cabochons not have this issue? I have an amethyst cab. When I tilt it, it changes from dark purple to light purple, without forming a dark hole.

I was also wondering, do sleepy gems (e.g. moonstones, chalcedony, rose quartz), faceted or not, usually have an obvious tilt window?

 

[T L]

Well garnets have a lesser tilt window, but if you don't want any noticable tilt window, diamond or sphalerite. I cannot see any tilt window on a well cut sphalerite, but it's a soft stone, not suitable for wear.

 

[LD]

Any faceted gemstone can have a tilt window. Generally the lighter the gem, the more obvious. However, I've seen some quite dark gems that exhibit one. Personally I wouldn't worry about tilt windows. They're acceptable in coloured gemstone world!

Cabs don't have them because they're not faceted and it's the placement of the facets that causes tilt window.

 

[chrono]

In short, the higher the RI, the less obvious (or rather, the greater an angle is needed to show) a tilt window. Cabochons are spared this window tilt because they are not faceted.

 

[cookies]

Cabs don't have them because they're not faceted and it's the placement of the facets that causes tilt window.

I didn't know this..thanks!

 

[kenny]

In short, the higher the RI, the less obvious (or rather, the greater an angle is needed to show) a tilt window. Cabochons are spared this window tilt because they are not faceted.

Hmm, I'm gonna stick my neck out here.
Curved or faceted shouldn't matter on this one.

Besides the IR (how much light changes angle as it enters or exits the stone) it is about the angle between the light ray and the surface at the point it enters and exits the stone's surfaces, not whether those surfaces are flat or curved.
A curve could be seen as just a million slightly different angles, and I'm pretty sure if you looked closely enough (we're talking microscopes) that is what is happening on curved stones.
Perfect curves are hard to make, in fact one space shuttle mission experimented in making more perfectly-round ball bearings without the influence of gravity.

Each point on a curve is not curved when you look closely enough and I believe light rays are very very small.

I'm just going with my gut here but would love to hear other perspectives on this.

 

[VapidLapid]

Kenny those are exactly some of the criteria I was thinking about when I made this design and cut this stone

[URL='https://www.pricescope.com/community/threads/vapithyst.152668/']https://www.pricescope.com/community/threads/vapithyst.152668/[/URL]

the top appears to be en cabochon though I think of this curved surface as being and infinitude of facets. The proportions were chosen to emulate normal (whatever that is) crown height and angles. The great variance from a cabochon is that I cut a full pavilion, which is an idealized paraboloidialoid. I call it that because I generated the paraboloid so that it would fit under the crown AFTER I removed the central portion of the parabola that was less than the critical angle for the material. with that center section removed the remaining sides were slid together. I cut a bit/scraper from that template out of 1/8" thick sheet of aluminum and sharpened the edge. That was in turn mounted in my drill press and was used to cut the paraboloidialoid negative shape in a block of tin. That was then charged with diamond powder, lubed with olive oil (Trader Joe's Extra Virgin) and the stone was ground against that to make the pavilion. Similar process for the crown but a rotated circular section generated the spherical section.

 

[Michael_E]

Personally I wouldn't worry about tilt windows. They're acceptable in coloured gemstone world!

I had to get a big chuckle out of this comment. They have to be acceptable, because they are unavoidable. All gems show tilt windows and all of the commonly used natural gems will show a tilt window if they are tilted at 16° or less. Zircon will show at 16° and beryl at about 2.5°. The only way to reduce the appearance of a tilt window is to make the crown smaller and in the medium to tall range. The pavilion angles of a stone are usually designed to get the best angles for reflecting light around your head and back to you eyes without getting to much of a reflection of your head in the picture, when you are looking directly at the table of the stone.

The critical angle and tilt windows are usually a secondary consideration, with tilt windows being only remotely affected by pavilion angles. This is because you can't do anything about the appearance of a tilt window when looking through the table of the stone and trying to affect the appearance of a tilt window with pavilion angles usually ends up giving a very poor appearance when the stone is viewed face up. The design of the crown of a stone plays a bigger part since a tilt window shows first and most prominently through the table. Making the table smaller and the crown a bit higher gives a smaller tilt window and better color as well, since light travels farther through the stone. As in everything, this is a trade off, since high crowns in dark stones can make them overly dark. Always a set of compromises, but then that's just the way reality is...you can't have your cake and eat it too.

 

[LD]

Personally I wouldn't worry about tilt windows. They're acceptable in coloured gemstone world!

I had to get a big chuckle out of this comment. They have to be acceptable, because they are unavoidable. All gems show tilt windows and all of the commonly used natural gems will show a tilt window if they are tilted at 16° or less. Zircon will show at 16° and beryl at about 2.5°. The only way to reduce the appearance of a tilt window is to make the crown smaller and in the medium to tall range. The pavilion angles of a stone are usually designed to get the best angles for reflecting light around your head and back to you eyes without getting to much of a reflection of your head in the picture, when you are looking directly at the table of the stone.

The critical angle and tilt windows are usually a secondary consideration, with tilt windows being only remotely affected by pavilion angles. This is because you can't do anything about the appearance of a tilt window when looking through the table of the stone and trying to affect the appearance of a tilt window with pavilion angles usually ends up giving a very poor appearance when the stone is viewed face up. The design of the crown of a stone plays a bigger part since a tilt window shows first and most prominently through the table. Making the table smaller and the crown a bit higher gives a smaller tilt window and better color as well, since light travels farther through the stone. As in everything, this is a trade off, since high crowns in dark stones can make them overly dark. Always a set of compromises, but then that's just the way reality is...you can't have your cake and eat it too.

Glad I made you chuckle! It's good to have a laugh a day!

I guess I was trying to put into perspective that coloured gemstone world doesn't equate to diamond junkie world where angles, facets, etc are scrutinised to the enth degree! We're a far less fussy bunch and go for colour all the way (normally)!!!