Ellyn is right; you need to avoid salt with anti-caking chemicals or iodine for best results. If you can find fine-grained kosher salt without anti-caking agents (a very few do have anti-caking agents), that will work. If all you can find is coarse kosher salt, you can process it in a coffee grinder or spice mill until it's finer. The reason you want it fine is so it will dissolve more quickly. There's a bit more info here: http://nchfp.uga.edu/how/can_06/salts_pickling.html

It is best to use canning (pickling)salt or kosher salt, if you have a tough time finding canning salt. (the less course, the better, if you use kosher salt). Pickling salt is similar to table salt, but doesn't have the iodine and anti-caking additives that turn pickles dark and the pickling liquid cloudy. Pickles would still taste good - just wouldn't look as great!