A discontinued pen from Platinum’s ReCelluloid range of, well, celluloid pens.
From online searches, this pen was seems to date from the mid-1980s to mid-1990s. Lambrou’s “Fountain Pens of the World” lists similar pens (going by nib design) from around 1992.
The celluloid used resembles the striated celluloids used for the Parker Vacumatic:
It even has semi-transparent strips alternating with opaque, slightly pearlescent ones:
Platinum makes the ReCelluloid pens by rolling thin celluloid sheets, rather than by turning celluloid rods on lathes. The former saves money and manpower, but the pen ends up with a distinct line where the edges of the sheet meet.
This pen has a different feed (left) from current production pens (right). Could it be ebonite?
Its music nib (left) seems a touch springier and smoother than the one on a more recent Platinum #3776 Balance (right):
Writes very nicely with Sailor’s Waka Uguisu ink. According to the seller, this one was a dry writer. If you’ve a Platinum pen and have similar thoughts, you might want to try a Sailor ink before adjusting the nib.
On a side note: on page 115 of Nakazono’s “Fountain Pens of the World” (not to be confused with Lambrou’s far more comprehensive work), there’s a circa 1931 Dunhill-Namiki plunger-filler with an almost-identical shape and similar-looking celluloid with silver instead of brown rings. An inspiration for Platinum’s pen designers?