Vintage Seiko Tank Gold-Plated — 5P31-5D40 (1988)

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Seiko rectangular gold-plated: the ultra-thin Japanese dress watch with a gilded dial

This Seiko watch is a dress watch designed for both women and men, conceived in the classic vocabulary of the shaped watch. Its rectangular case, gold-plated, with polished flanks and slender lugs, favors wardrobe elegance rather than presence. The case measures 24mm (25mm with the crown) for a Lug-to-lug of 33mm and a thickness of only 5.9mm, Crystal included. A slim piece, made to slip under a shirt cuff.

The gilded dial has, over time, taken on a marbled patina that gives it the character of a lived-in piece rather than the smoothness of a new dial. Applied gilded baton indexes punctuate the periphery, doubled at 12 o'clock, and two fine faceted hands are sufficient for the display: no seconds hand, no date. The Seiko signature occupies the top of the dial, the reference engraving the bottom. It is a two-handed watch, as pared down as possible.

Inside beats the Seiko calibre 5P31, an analog quartz movement produced in Japan from 1987 onward, used on the brand's dress lines. Its slim construction, without a seconds train, is precisely what allows the watch's 5.9mm profile. The movement of this example has been checked by our watchmaker and the battery replaced before shipment. Seiko has not published a precision specification for this calibre: we therefore make no numerical claim.

On the wrist, the piece behaves like a de ville jewel. The warm gold plating and compact format place it in the register of tuxedo watches, here enhanced by a genuine crocodile leather deep green strap that contrasts beautifully with the gilded case. This strap is not original; it is fitted with a steel pin buckle. The Lug width of 19mm leaves every possibility of changing it.

Three points to note

• The gilded dial shows a marbled patina and diffuse signs of oxidation, visible up close: an age mark that we prefer to disclose rather than embellish.
• The 5P31 calibre is no longer produced: movement parts are becoming harder to find, but a battery change remains a routine operation for any watchmaker.
• The case is gold-plated, not solid gold: it calls for avoiding repeated friction against a bracelet or a Buckle buckle.

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Technical specifications

• Brand: Seiko
• Model: Rectangular dress watch
• Reference: 5P31-5D40
• Serial number: 840xxx
• Year: 1988 (April)
• Origin: Japan
• Gender: Men's and women's watch (Unisex)
• Movement: Japanese quartz, Seiko calibre 5P31
• Functions: Hours, minutes
• Case: Gold-plated (steel case back), rectangular shape
• Dimensions: 24mm (25mm with the crown)
• Lug to lug: 33mm
• Thickness: 5.9mm (Crystal included)
• Lug width : 19mm
• Crown : Gold-plated, fluted, original
• Dial : Gilt with mottled patina, applied gilt baton indices, original
• Hands : Faceted gilt baton hands (hours, minutes), original
• Crystal : Mineral, very good condition
• Bracelet : Genuine green crocodile leather, not original
• Buckle : Steel buckle, not original

Condition and warranty

• Overall condition : Good condition. Case with a uniform gold-plated finish, with some wear along the edges. The gilt dial, however, shows a mottled patina and diffuse signs of oxidation, consistent with the age of the piece and accepted as such.
• Water resistance : Not guaranteed (vintage watch)
• Authenticity : Lifetime guarantee
• Mechanical : Checked quartz movement, new battery, guaranteed for 1 year
• Included : Atelier Victor invoice, protective case
• Not included : Original box and papers

Frequently asked questions

Is this rectangular Seiko a Cartier?
No. This is an authentic Seiko, signed on the dial and engraved with its reference 5P31-5D40. The rectangular gold-plated case with gilt dial belongs to the common vocabulary of dress watches from the 1980s, adopted by many Japanese and Swiss houses. This piece claims nothing other than what it is, and the authenticity of its brand is guaranteed for life by Atelier Victor.

Is the Seiko 5P31 caliber reliable?
Yes. The 5P31 is an analog quartz movement produced in Japan from 1987 for Seiko dress watches. Its simple two-hand construction makes it durable, and in practice servicing is limited to battery replacement. The movement of this example has been checked by our watchmaker and is guaranteed for 1 year.

Is dial patina a defect?
No, it is a trace of time. On vintage gilt dials, oxidation over the years creates marbling and nuances that give the piece its character. We disclose it with full transparency: it is up to you to appreciate this dial for what it is, a lived-in surface, not a refinished dial. This patina has no effect on the watch's performance.

Is this Seiko 5P31-5D40 water-resistant?
No. Water resistance is never guaranteed on a vintage watch: the original seals have aged and the pressure of the caseback is no longer what it once was. Avoid the shower, the pool, and the sea. A simple contact with rainwater, however, does not pose any difficulty.

Does a 24mm rectangular case suit which wrist?
On a rectangular watch, it is the Lug-to-lug that matters: 33mm here, which places the piece on wrists from 14 to 18 cm. It is the classic format of the shaped dress watch: discreet on a masculine wrist, perfectly proportioned on a feminine wrist. Its 5.9mm thickness allows it to slip under a cuff.

A piece selected by Atelier Victor

Authenticated, checked, and photographed by us. As all sales are final, our team remains available 7 days a week on WhatsApp to answer your questions, share additional photos or a video of the piece in hand — so that your choice can be made with complete peace of mind.

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