The plates are inspected after leaving the grinding room, and if any scratches or defects of any kind are found they are marked. Some of these can be rubbed down by hand. There are also, not infrequently, nicks and fractures found at this stage; and in such case the plate must again be cut and squared. Afterward comes the polishing, which is done on another special table. The polishing material is rouge, or iron peroxide, applied with water, and the rubbing is done by blocks of felt. Reciprocating machinery is so arranged that every part of the plate is brought underneath the rubbing surface. The grinding and polishing has taken away from the original plate half of its thickness, sometimes more. There is no saving of the material; it has all been washed away. When to this waste is added the fact that fully half of the original weight of lime and soda has been released by the heat of the furnace, escaping into the atmosphere in fumes and acids, one may begin to understand something of the cost of converting the rough materials of sand, limestone and soda into beautiful plate glass. ~HOW MIRRORS ARE MADE~ In preparing plate glass for mirrors great care must be exercised in the selection of the plates. This selection bears reference not only to surface defects, but to the quality in general; defects which cannot ordinarily be seen are magnified many fold after the glass has received a covering of silver. [Illustration: BEVELING PLATES] In the process of beveling, the plate passes through the hands of skilled workmen of five different divisions, namely: roughers, emeriers, smoothers, white-wheelers and buffers; and different abrasive materials are used in the order indicated by the titles. These materials are sand, emery, natural sandstone imported from England, pumice and rouge. The roughing mill is a circular cast-iron disk about 28 inches in diameter, constructed so that the face or top of the mill revolves upon a horizontal plane at a speed of about 250 revolutions per minute. The sand is conveyed to the mill from above through a hopper simultaneously with a stream of water which is played upon the sand to carry it to the mill. The rougher places the edge of the plate upon the rapidly revolving mill, and the cutting of the bevel is done by the passage of the sand between the mill and the plate of glass. A bevel of any desired width may be produced. Pattern plates containing incurves, mitres, etc., require a practiced eye and great skill upon the part of the operator.