Large Dutch silver shell-shaped pendant watch Circa 1700

Silver and rock crystal verge with date 
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A large Dutch silver and rock crystal shell-shaped verge pendant watch with date, circa 1700. Round brass full plate movement, chain and fusee, verge escapement, three-armed brass balance.
Silver champlevé dial with Roman hours, Arabic minutes, blued centre with applied silver ornaments, date indication, finely cut hands. Engraved case frame, hinged and grooved rock crystal cover and back.
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Diameter: 55 mm
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Weight: 203 g
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Signed: Jacob Ratsma Amsterdam
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Jacob Ratsma came from a large family of smiths and watch- /clockmakers. He donated a town clock to Harlingen in exchange for the position of town clockmaker for himself and his descendants. His son Tjeert Jacobsz Ratsma (1696-1781) of Harlingen was particularly successful as a maker of timepieces. He went to Amsterdam as a young man to learn the trade and after his training he returned to Harlingen as a master watch- and clockmaker.