More commonly called ammonia solution, or just ammonia, ammonium hydroxide is often diluted for use in household cleaning agents, including window glass cleaner formulas. It is typically sold plain with an added lemon or pine scent and yellow coloration to distinguish it from other household cleaning agents. When soap is added, the mixture is often referred to as cloudy ammonia. Industrially, ammonium hydroxide is used as a precursor for various alkyl amines, though the preferred precursor for this process is usually anhydrous ammonia. Furniture makers also use ammonium hydroxide to darken or stain wood rich in tannic acid. When sealed in a container together, the ammonium hydroxide fumes react with the tannic acid and iron salts that are naturally occurring in most hardwoods, creating a rich, dark stained appearance. In the food industry, ammonium hydroxide is used as a leavening agent and as an acidity regulator, and its pH control abilities make it an effective antimicrobial agent as well.