Many household products contain lye, the chemical sodium hydroxide. Lye is a caustic, alkaline chemical, which means it dissolves sticky substances like fat, and has a high degree of reactivity with other materials. Lye, in a flake, granular, or liquid form, is very dangerous and can cause damage to surfaces and people. Lye is created out of a chemical reaction between soda, known as sodium carbonate, and calcium hydroxide, or lime. In raw form, it's made into solid flakes, chips, or grains. Chemical suppliers provide lye to manufacturers to make a wide variety of products, such as fabric, paper, personal soap, laundry detergent, pool-cleaning supplies, metal polishers, and drain de-cloggers. Since households utilize so many poisonous products, they must take care to keep cleaners out of the reach of children and only use them as directed. For instance, carefully follow the directions to clean a sterling silver gravy boat with lye-based polish, because even the fumes can be dangerous. Never use products like drain de-clogger or paint stripper without enough air circulation. Caustic lye products pose other dangers to surfaces. They can dissolve substances to your advantage, like hair clogs in a shower drain, as well as to your detriment, such as the adjacent shower curtain. In fact, lye can damage and corrode paint, metal, cloth, plastic, and especially skin. Lye can be so reactive that, in its solid form, it should be kept away from metals, such as aluminum, and the open air. It's usually non-combustible when dry, but could ignite when mixed with water and cause a fire. Before the modern manufacture of lye, people were able to make it out of raw materials. For thousands of years, people have used lye for soap making and tanning hides. They burned certain hardwoods at a very high temperature to make white, not gray, ashes. Apple trees, oak, and seaweed kelp make ideal fuels. Then water, mixed with a bit of baking soda, penetrates the ashes and removes the lye they contain. When the ashes are filtered out, the water holds enough lye to dissolve fat left on animal furs, or to mix with other ingredients to make strong body soap.