In a medium, nonreactive saucepan over low heat, warm the vinegar just until it begins to give off steam (do not bring to a boil).
Put 1 pint of the raspberries into a fine sieve fitted over a sterilized 1/2-gallon clamp jar.
Pour the warm vinegar over the berries and let it run into the jar, then add the berries to the jar.
Allow the mixture to cool 20 to 30 minutes to room temperature, then seal and shake the jar gently.
Set the jar out of direct sunlight and away from heat to steep for 4 days, shaking it every so often. While steeping, the vinegar will take on a raspberry hue and the fruit will lose most of its color.
Strain the mixture through a fine sieve into a large batter bowl with a handle or into a large, nonreactive saucepan.
Rinse the jar and return the strained vinegar to it. Rinse the bowl or saucepan.
Dump the fruit and rinse the sieve. Dampen a flat-bottom coffee filter, then line the sieve with the filter and fit it over the bowl or saucepan.
Transfer the vinegar to flasks or bottles. Discard fruit.
If you wish, spear 6 to 8 whole raspberries on a wooden skewer and put the skewer into the container before filling.
The vinegar should be ready to use immediately, with a shelf life of at least 1 year.
VARIATION: For Raspberry Lemon Thyme Vinegar, place 1 sprig fresh lemon thy me in a flask or bottle before adding the vinegar. Fill, seal, and steep out of direct sunlight and away from heat for 1 week before using or shipping.
CRANBERRY VINEGAR Follow the recipe for Raspberry Vinegar, except substitute 4 cups (1 pound) fresh cranberries, coarsely chopped, for the raspberries. Decorate, if you wish, with skewers of whole cranberries.