Breakage can be avoided by ensuring that, where the sizes of the sheets are large, the crates or cases are stiffened sufficiently so as not to bend slightly when being handled or slung. Care should also be taken to see that the sheets of glass are properly chocked off in the cases or crates, as any negligence in this respect may result in damage to the sheets. Large sheets should be slung and handled on their edges. In all circumstances, to avoid breakage, packages of glass should be kept in the upright position and never allowed to lie on the flat
A common form of damage to glass is staining, and a frequent cause is either dampness in the packing when shipped or dampness which has been absorbed by the packing during course of transit. There are various methods by which these stains may be removed. One suggestion is that the glass be polished with red iron oxide. Another suggestion is that a suspension of precipitated chalk in 2% solution of ammonia be rubbed on the glass, the glass finally being cleared by rubbing with a 5% solution of chromic acid. It is suggested that this latter treatment should be confined to figured glass. It is also suggested that buffing might offer some improvement if used for figured glass, provided that a very soft cloth buff is used which will penetrate the grooves in the pattern. Some improvement could, however, be obtained as a general rule by scrubbing the surface with a fairly hard brush, the brush being dipped in a solution of acetic acid. For commercial purposes a good vinegar would be quite satisfactory. The acetic acid or vinegar will dissolve the small amounts of lime and soda which hold the silica fairly firmly on the surface of the glass, and, provided the staining has not gone too far, will effect a considerable improvement in the appearance. The treatment of rolled figured glass or window glass with hydrofluoric acid, as a means of removing stain, is certainly not recommended. The hydrofluoric acid will dissolve the stain material, which is mainly silica, but it will tend to produce a light gray etching over the whole surface. The grayness will depend on the exact composition of the glass, on the strength of the hydrofluoric acid, and on the length of time during which the hydrofluoric acid is in contact with the glass surface. The process is dangerous, because even very dilute hydrofluoric acid can cause severe injury to the skin; also, unless the process is very carefully controlled, the etching can produce a sufficiently noticeable gray for the condition of the glass to be worse than at first, except perhaps that the gray might be more uniform over the whole surface.
The following have been recommended by experts as the most satisfactory methods of dealing with staining:
Figured class - Stains caused by water or dampness, provided the attack on the glass is not too severe, may be removed by treatment with a hot detergent solution.
Plate glass - Certain manufacturers consider that the only satisfactory method of removing stains from plate glass is by repolishing with rouge or cerium oxide. This is preferably done on a special machine, but may also be done by hand.
Sheet glass - The expense of repolishing is usually not justified in the case of sheet glass, but it may be treated in the same manner as recommended for figured glass, provided again that the attack on the glass is not too severe.
Optical goods - Mold formation may result in glass being etched as if it had suffered from scratching. If doubt exists as to cause of scratching an expert's opinion should be sought.
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