Many companies install privacy glass doors in restrooms, and other places where commercial interior glass doors need to be opaque. These doors are made from panels of the finest soda-lime glass, that has been heat strengthened, or tempered to withstand the temperature fluctuations that can occur, as well as to insure that if the panels are broken they will crumble into small pieces, rather than break into large pieces.
To heat strengthen a glass panel the manufacturer must first create the panel to their customers exact specifications. The holes to allow hinges, door knobs, locks and other such hardware to be attached to the finished product must be pre-drilled before the piece is put through the tempering process. The manufacturer must be certain of the exact size as well, because once a panel of this fragile material has been heat strengthened, the cutting of it becomes almost impossible. Generally the result of attempting to cut, or drill a hole into tempered glass leaves you with a broken mess to clean up.
To heat strengthen these fragile panels the manufacturer must reheat the prepared soda-lime glass to the verge of melting it, then they cool the glass down very rapidly. After this is done the material is changed from a fragile substance that will break into large irregular pieces to a substance that can withstand up to 10,000psi of compression before you could break it. After the process, once broken the material will not crumble into small pieces that will not be capable of cutting someone to the point of their needing stitching up, or until they are grievously injured.
The next thing the manufacturer has to do is to rough up one side of the panel to create an opaque look that is difficult to see through. With these large pieces this is usually done by using a sand blasting technique. The manufacturer will use a special piece of equipment to propel tiny bits of hard substances at the panel to create a white, or opaque side to the panel. The worker applying the roughened side can turn their equipment ever so slightly and cause different shadings to appear, or to create different visual effects on the panel.
While this process is called sand blasting, sand is not the only material that is used to create the effect. Sand was once the most widely used material, but workers developed severe lung problems from breathing in the dust created by the silica. The different manufacturers started using pieces of walnut shells, pieces of coconut shell, slag pieces, copper pieces, and all manners of hardened materials to whiten the glass panels. All workers who perform this operation now wear protective gear, in well ventilated rooms, so they do not damage their lungs as they did in the first days.
Once the piece is tempered, and roughened to create an opaque side, it is ready to be installed in areas of public domain that require a reduced visibility in the glass pieces.
