I don't get to add pens to my primary Parker collection much due to the cost of the ones I have left to add. However, I have been on the hunt for a celluloid JKS for years and one finally came up on ebay, mismarked as a Bakelite pen. I sniped it high to make sure I got it, and managed to pay what would be appropriate for a Bakelite, which was fine by me.
The key "tell" that this is celluloid is the yellow on the thread ends. This is the typical color of the Parker celluloid barrels. However, they tend to discolor into a reddish color that's similar, but not as dark as, the Parker Bakelite barrels. In addition, there's no sign whatsoever of the "BAKELITE" barrel imprint.
The barrel has really nice transparency in person, where you can easily see the pressure bar and the silicone sac that someone recently added. I'll leave it in there since it works well as a "demonstrator" (which this isn't).
So, to rip off David, this is a "happy John" moment.
