Star Sapphire: Low vs High Dome

Dreamer_D · Mar 20, 2023

I am on the hunt for a lovely star sapphire for a ring project. Thanks to the many knowledgeable folks who have posted their gems in this forum, and especially the wonderful “Show Me Your Star Sapphires and Rubies” thread, I feel like I have been able to find answers to most of my questions. But I haven’t been able to find an answer to this one!

I have noticed some star cabs have very bulbous domes, and especially many of the large and highly valuable specimens I have seen here. But many also have much lower domes with just a slight convex. My question is: what effect does dome height have on the optical properties and value of a star gem?

Starstruck8 · Mar 20, 2023

dreamer_dachsie said:
I am on the hunt for a lovely star sapphire for a ring project. Thanks to the many knowledgeable folks who have posted their gems in this forum, and especially the wonderful “Show Me Your Star Sapphires and Rubies” thread, I feel like I have been able to find answers to most of my questions. But I haven’t been able to find an answer to this one!

I have noticed some star cabs have very bulbous domes, and especially many of the large and highly valuable specimens I have seen here. But many also have much lower domes with just a slight convex. My question is: what effect does dome height have on the optical properties and value of a star gem?

The main difference is how much the star moves as you turn the stone. With a low dome, small turn of the stone gives big movement of the star. WIth a high dome, the star doesn't move as much. Put differently, with a low dome, the star dances, with a high dome, it's more stable. I have no particular preference, except maybe to avoid extremes.

Haven't noticed any relation to price. Usually other factors like brightness and sharpness of the star and translucency, uniformity and colour of the body are more important.

LilAlex · Mar 21, 2023

@Starstruck8 is more knowledgeable but I have never seen an exceptional low-dome star sapphire. With good translucency or even transparency, you need to be looking through a fair amount of material.

Too high/tall can be drawback in terms of wearability and "floppiness" but less so for a woman's ring. I love a true sugarloaf but those can be quite pointy and the star can be hard to make out. All in all, I prefer a Goldilocks dome that is "medium" height.

I have an opaque gray with a razor-sharp star but it is a low-ish dome and a terrible sapphire (objectively, a polished rock). Spouse has a translucent purple with a high dome but not a sugarloaf. Side view, below, to show the shape; it's kind of a double-cab gumdrop. This is pushing the limits of wearability but she wore it to work so I guess she could still type and put on gloves.