Chinese black vinegar is a dark complex, mild vinegar made of glutinous rice and malt somewhat similar to a balsamic used in Chinese stir-frys, braises, and sauces. Black vinegar is from the Chinkiang Province of China. This is a traditional ingredient in sharks fin soup.

Sweetened Black Vinegar
There are two types of Chinese black vinegar sold. One will be labeled "Black Vinegar" and the other is "Sweetened Black Vinegar". Sweetened black vinegar is very different and has added sugar and flavorings, usually including ginger. This ingredient is used primarily for braised pork dishes. Do not use the sweetened vinegar to replace regular black vinegar.

Where To Buy
You can find this vinegar in many Asian markets as well as online here at Amazon.com. Chinese Black Vinegar

Substitute For Chinese Black Vinegar
Clearly, the best thing to do is to find the black vinegar, but if that's not practical, then there are some options that will produce acceptable results. This is particularly true if you've never had the real ingredient, to begin with:

Substitute equal parts of date vinegar, similar in color but sweeter
OR - Balsamic vinegar, which is a good choice because it's likely you may have it in your pantry; it is similar in color but still sweeter than black vinegar.
OR - Red rice vinegar + small amount of superfine sugar
OR - Balsamic vinegar with a splash of Worcestershire sauce, which helps to cut the sweetness.
OR - One home chef suggests success using malt vinegar to replace the black vinegar.
OR - Per tablespoon needed, combine 1 tablespoon water, 1 1/2 teaspoons balsamic vinegar, and 1 1/2 teaspoons rice wine vinegar.