Glass Sheets

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Usually shipped in crates or cases. Much breakage can be avoided by ensuring that, where the sizes of the glass sheets are large, the crates or cases are stiffened sufficiently so as not to bend when being handled or slung. If the case is not fitted with skids/cleats but is still to be pushed about by fork-lift trucks in ship’s hold during loading and stow-tightening operations, the lower part of the cases should be faces with a hardwood batten to reduce the risk of fork prongs penetrating the case and contents. Glass must be packed securely within the case to prevent movement, this chocking can be achieved by generous use of wood wool, polystyrene, etc., packing materials. Usually the glass stands on strips of material proud of the base of the case. The support material must not compress unduly when the case is mishandled, for example snatch lifted/dropped, otherwise scratching or breakage may result. Where large sheets are concerned, they should be slung and handled on their edges. In all circumstances, to avoid breakage, packages of glass should be kept in an 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 transit. When glass is shipped overseas in cases, however, it will normally be interleaved with paper or other interleavants and either the glass block will be wrapped in paper/polythene or the case will be so lined to prevent moisture ingress. There are various methods by which stains may be removed but they all require long and laborious treatment by at least semi-skilled labour and so are seldom economically justifiable for ordinary glass products. No treatment can remove severe stain, and even light stain cannot be removed so successfully that the glass could be subsequently silvered.
One suggestion is that the glass be polished with red iron oxide another 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 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, providing that 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 not recommended. The hydrofluoric acid will dissolve the stain material, which is mainly silica, but it will tend to produce a light grey etching over the whole surface. The greyness will depend on the exact composition of the glass, on the strength of the hydrofluoric acid and the length of time which it 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 grey for the condition of the glass to be worse than at first, except that the grey might be more uniform over the whole surface.

Float glass is used extensively in the building industry for windows and building facades. It is shipped in wooden crates with inner packaging of wood wool, polystyrene, straw or other soft packing. The quality of the crates is crucial and they must be of solid stout construction to protect what is a delicate cargo.

Risks include the following:

• Glass is prone to stain damage resulting from dampness working into the packing. Whilst stains can be removed it can restrict its future use. • Due to the fragility of the cargo, proper securing is essential to prevent damage. • Care must be taken to avoid uneven distribution of weight on container floors resulting from point loading of crate pads or skids. • In the event of cargo being “out of gauge” any rail or road movements should be checked for bridge clearances. • Float/sheet glass must never be stowed flat and must always be on end.

See stowage instructions for slab marble which also apply to glass. In particular the stowage on “A” frames should be noted.