Diffusion Stones, or 'Air Stones', are commonly used to aerate wort before fermentation, which helps ensure a healthy start to the fermentation process. Diffusion Stones can be attached to compressed oxygen tanks or air pumps (such as those used with aquariums). This "Stone" is made of stainless steel, so it's durable, easy to clean, and won't crumble in your wort after a few uses like other materials! The ½ micron stone produces very small bubbles, which are ideal for efficient absorption of the gas into your wort. However, it takes more pressure to force air through the smaller pores. This is not a problem when using compressed oxygen, but lightly-powered air pumps may not work well. The Diffusion Stone is also suitable for force carbonation of beer inside a keg, where the faster absorption of gas achieved by the small, ½ micron pore size is a great advantage.