1 medium pineapple, peeled
4 medium kiwi, peeled
12 medium strawberries
12 large seedless red or green grapes
1 3/4 pounds semisweet chocolate (62 percent), cut into small chunks
3 1/2 ounces white chocolate, cut into small chunks
special equipment: 12 (8-inch) wooden skewers; a candy thermometer; parchment paper
Line a baking sheet with parchment paper. Fill a medium saucepan with 2 inches water; bring water to a simmer.
Meanwhile, cut 12 1-inch chunks from pineapple (reserve remaining fruit for another use). Cut 12 1-inch chunks from kiwi. Thread 1 piece pineapple, 1 piece kiwi, 1 strawberry and 1 grape onto 1 skewer. Repeat with remaining fruit and skewers.
Fill a large metal bowl with ice and cold water; set aside. Put ⅔ of the semisweet chocolate into a metal bowl fitted with a candy thermometer. Set bowl over (but not touching) the simmering water, and, stirring occasionally, heat until chocolate reaches 115º. Remove bowl from heat (leave simmering water on), add remaining semisweet chocolate, stir until melted, then chill over ice bath, stirring constantly, until temperature reduces to 84º. Return bowl to pot of simmering water and heat, stirring occasionally, until chocolate reaches 88º to 89º (chocolate is now tempered). Remove bowl from heat and immediately spoon chocolate over 1 fruit skewer, turning skewer to coat. Repeat with remaining skewers.
Put white chocolate into a medium metal bowl. Set bowl over (but not touching) the simmering water, and heat, stirring occasionally, until chocolate is melted. Transfer chocolate into a small resealable bag. Press out air and seal bag, then, using scissors, make a tiny snip in 1 corner of bag and gently squeeze chocolate toward corner. Pipe chocolate over skewers to create decorative lines. Let stand at very cool room temperature until chocolate is set, 4 to 6 hours.