NOTE: When selecting cucumbers for pickling, there are a few things to remember. For crisp pickles, choose ripe, pickling cucumbers, which are shorter and chunkier than regular eating cucumbers, which tend to be longer and smoother. Ripe pickling cucumbers are darker green, firm, and not "bloated." They should have plenty of spiny bumps on the outer surface. Overripe cucumbers make mushy pickles. They tend to have yellow or white streaks or spots and their surfaces are smoother. Choose pickles that have not been coated in wax, as the pickling brine cannot penetrate through the wax. The fresher the cucumbers, the crisper the pickles will be. For best results, try picking your own cucumbers from a local farm or farmers' market.
Combine the vinegars, sugar, mustard seeds, turmeric, cloves, garlic, and peppers in a medium saucepan over high heat. Bring to a boil, reduce heat to medium and add the cucumbers and onions. Bring to a simmer and remove the saucepan from the heat.
Fill each of the hot sterilized pint-size preserving jars with the pickle mixture, dividing them evenly, and enough of the liquid to come within 1/2-inch of the top. Add 1/2 teaspoon of Natural Pickle Crisp to each jar, if desired. With a clean damp towel, wipe the rim and fit with a hot lid. Screw on the metal ring just until the point of resistance is met. Process the jars in a hot-water bath for 15 minutes.
Using tongs, remove the jars, place on a towel, and let cool. Test the seals by allowing the jars to stand at room temperature overnight or until the lids pop. Tighten the rings and store in a cool dry place. Let the pickles age for at least 2 weeks before using.