You can get a lot done in a day. You can fly to London and back twice. You can bake 24 lemon cakes. But you cannot create a piece of jewelry.

At least not if you’re designer Jennifer Kobrin, who takes up to 25 hours to complete her painstakingly detailed bracelets, necklaces, earrings, and rings. (One assumes she has time on her hands to keep track.)

The SF-based artist holes up (as in minimal e-mails and phone calls) to work on her handmade casts and molds. She’s inspired by nature and the macabre, and the results are hauntingly beautiful. Lace cuffs based on swatches of antique Venise fabric are dark yet ladylike. Oversize feather rings make elegant knuckle-dusters.

Her stuff doesn’t come cheap.

Then again, Rome wasn’t built in a day either.

Available at MixedUse, 463 Union Street, between Grant Avenue and Kearny Street (415-956-1909 or mixedusemodern.com). Ver Unica, 437b Hayes Street, between Gough and Octavia Streets (415-431-0688 or ver-unica.com). For custom pieces, call 415-596-1429 or email jenniferkobrin@yahoo.com.