Volcanic Rock is Your Friend
Pumice can be a very versatile abrasive for use with glass. Unlike loose abrasive like silicon carbide or aluminum oxide, pumice is a very friable abrasive that allows you to achieve a very fine surface grind on your glass. It can be used to give a pre-polish finish on your glass from a fine grit surface or even achieve a near polish on your glass without the use of cerium. Pumice can be used with a brush wheel or MJ wheel on a lathe, it can be used by hand with a Scotch-brite pad, it can be used with a cork belt on an upright belt sander, and it can be used with a felt pad or cork pad on a flat lap grinder as well. It's a highly versatile abrasive that can be utilized with virtually every type of cold working equipment.
Just like any other loose abrasive you may use in your coldworking shop like silicon carbide or aluminum oxide, Pumice can very easily become airborne in your coldworking use and create a cloud of the abrasive in the air while mixing or using the pumice. It is vitally important to follow safety shop rules when using abrasives like pumice. Never work with pumice without using a respirator or vacuum filtration system. Be sure to also clean your work area at the end of the day to be sure not to leave piles of pumice around on your equipment or work space that can become airborne later on.
Making mud pies
Pumice sits between loose abrasives like silicon carbide and cerium not only in it's abrasive quality on your glass, but also in how it is mixed and used with water. While silicon carbide is used with water to create a loose slurry for grinding your glass and cerium is used with water to make an almost liquid slurry for use with felt to polish your glass, pumice is mixed with water to form an almost mud like consistency in order to finish your glass surfaces. It's much finer than silicon carbide so it will mix with the water, but not as fine as cerium so it needs less viscosity in order to work well on your glass surfaces.
Brush up on Abrasive Grinding
One of the more common ways to use pumice is with a brush wheel on a lathe. The brush wheel allows you to get into hard to reach areas of your cast work to help polish up and clean up the surfaces without removing the distinctiveness of the piece. The rows of cactus fiber brush move in and around your piece while moving the pumice across the glass to abrade and clean the surface area gently. Brush wheels and pumice are a great way to quickly and efficiently accomplish finish work on your complex shapes.
Along with using a brush wheel or MJ wheel on a lathe, pumice can also be used on a cork belt, or a felt pad on a flat lap, or even by hand with a Scotch-Brite pad. For pieces that require more precise control you can easily mix pumice and use a Scotch-brite pad to gently abrade and work the surface of your glass into a lusterous glow.