A witch's bottle is a type of folk charm that is designed to attract and trap any negative energy or malicious magic sent your way*, so that it is prevented from causing you any harm. Witch bottles were a common folk charm used throughout the 16th and 17th centuries to protect people from negative magic; more than 200 witch bottles have been found buried throughout Europe, but most are broken by the time they are uncovered (Viegas, 2009). An example of an American witch bottle was found in Pennsylvania that dates to the 18th century, and the practice was common enough in America that preachers spoke out against its use, although it was also recommended by other contemporaries, including Cotton Mathers, as a good protection against witches (Becker, 2009). During a period when many people feared witchcraft the witch bottle offered a sense of security and protection and allowed people to proactively defend themselves when they felt they may be the victim of a curse. In modern practice a witch's bottle is still an excellent tool to use to protect yourself from any possible negative magic, rather like a magical electric fence.
Examining a witch bottle found in Greenwich that dates to the 17th century shows the contents to be similar to those that are still used today: urine, sulfur, nail clippings, nails, and pins (Viegas, 2009). Many examples of witch bottles also include a felt, cloth, or leather heart pierced by a pin as well, although the exact purpose of this is unknown (Becker, 2009; Viegas, 2009). It was believed that the pins and nails would turn the magic back on the caster, while the urine and nail clippings would draw the magic intended for the person to the bottle instead; often the ingredients would be boiled together first (Becker, 2009). Historical examples are found buried, often top down, in front of a house with the intent of protecting the home or a specific inhabitant from malicious magic (Becker, 2009). The bottles used were the type commonly seen in those areas for drinking and could be stoneware, ceramic, or glass, with a specific type called a "Bellermine" often used. The Bellermine was named after a Catholic cardinal whose face appeared stamped on the bottles.
In modern practice the bottles would be made and used in much the same way as they were historically. To make one you need a glass or ceramic bottle that can be corked or sealed at the top. For a basic bottle add your own urine and nail clippings, some hair, sulfur, nails and pins; if you want you can include the felt heart as well. The bottle can be modified with other materials such as herbs - Agrimony or Blessed Thistle work well for anti-curse magic, or for something stronger Mandrake or Belladonna could be used, for example-, broken glass, mirrors, or peppers. Add the urine first - on a practical note I recommend using a cup to collect it and then pouring it into the bottle - then add the other items. Traditionally the mixture would be boiled before being added to the bottle. Once the bottle is full seal the top, and if you'd like to, say something to charge the bottle with its purpose. When complete bury the bottle near the front of your home where it won't be found or disturbed; although some people who live in an apartment or otherwise have no land to bury it in might choose to keep it hidden under a sink or bury it in a potted plant inside the home. If you move do not disturb the old bottle (although if its under your sink don't leave it there!), rather make a new bottle for your new home.
* Many modern sites talk about using witch bottles for different purposes, along the lines of a charm. This may work well for others, but I stick to the traditional use - if I want a charm for money or love I'll just make one for that instead of using a witch bottle.
Becker, M., (2009) An American witch bottle. Retrieved from http://www.archaeology.org/online/features/halloween/witch_bottle.html
Viegas, S., (2009). 17-th Century urine-filled witch bottle found. Retrieved from http://www.msnbc.msn.com/id/31107319/ns/technology_and_science-science/t/th-century-urine-filled-witch-bottle-found/