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Kappa's Jewels

We'll start with the easy one - the right jewel.  Observe how while the comm is being opened by the mesmerized Yang woman at the end of The Omega Glory...

... the large dark green rhinestone's top suface flashes yellow, then a side facet shines cyan - telltale signs of an AB stone.  There's also Kappa's multiple appearances in The Enterprise Incident while Scotty is installing the stolen cloaking device:

That final flash of light blue from an otherwise green gem confirms the right rhinestone is a 20ss Emerald AB, like what's been commonly seen in many of the other comms.

The middle jewel, however, is more problematic.  It doesn't behave at all like the 8-sided rhinestone to its side.  No facets brighten up as the prop is being moved about.  Instead the red stays at a sedate glow until held at just the right angle where a bright inner-refracted highlight comes out.  If that's all we had, it'd still be a mystery.  Wonderfully, though, there's also the undated (presumably 3rd season) film clip from Lincoln Enterprises (courtesy of John Kious).  Note how the rounded center stone compares to a regular faceted rhinestone of the same diameter:

There's also a cap from Who Mourns for Adonais that verifies this tall center gem:

What's there on Kappa is not a faceted rhinestone but a "cabochon," a generic term for a smooth-surface gem.  A cabochon can be any shape; square, oval, round, or in this case a "bullette" (or "bullet"), and based on the Lincoln clip, it appears to be 3mm in diameter and about that tall.  At first blush, this might seem an inexplicable item, but there is a sensible lead as to its true source... in Wah's two tricorders, built a month after he did the communicators, he used intact Art Deco cabochon wristwatch winder crowns (and in fact one of them was red!):

Since Kappa's bare cabochon is mounted directly atop an Aurora hub, Wah must have excised the gem (a ruby or garnet) out from its metal base (easy to do) and simply glued it down on the comm:

For your replica, first try "garnet watch crown" on eBay, and maybe you'll get lucky, albiet likely for a price (the below is selling for almost $30 a pop):

Or if close is close enough, try on Etsy "garnet 3mm cabochons" or"bullets":

Lastly, the left jewel, or more accurately the lack of a left jewel, seems to have been purposefully done by Wah.  He was clearly running out of stones, as per the (desperate) use here of a watch crown cabochon.  No hint of a left gem is seen even in the earliest screencaps of Kappa's control well - below in The Man Trap and Tomorrow is Yesterday:

Nor is there in any image of this prop evidence of glue on the left hub's top.  He looks to have run out of time and stock and just kept that one blank.

Left

never installled

3mm red cabochon

20ss Emerald AB

20ss Blue Zircon AB

Wah cut out the Pattern #4 "spider" image from a loose-sheet advertising insert (a reprinting of a combined page 38 and 74 from the Edmund Scientific catalog) that came along with the 1964 moiré book - and put it into this prop:

A orange-ish glue stain seen on the paper insert...

... is figured to have been introduced not by Wah but from a mid-second season repair, where earlier (below, in "Who Mourns for Adonais?") the insert was pushed into the bezel ring on the right side:

More information on its moiré pattern can be found on our A Moiré Story page.  And a high-resolution print-ready scan of the original source material can be found here.
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We get a single look, in The Man Trap, at this comm's aluminum strip between the hinge wheels, terribly exposed and about to fall out.  This sighting supports our belief that Wah installed this part in all ten communicators, but obviously many were not glued in well and went quickly missing.

The front two are definitely slotted brass oval head, and the rear ones are likely the same:

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Note in the cap above what might be a ding (red arrow) in the midplate from some prior impact.  These spots are also seen in a cap from "Day of the Dove" below.

 

Note above at the red arrow the broken solder on the bent antenna wire out of the right hinge wheel.

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