It is possible that an erroneous idea of the strength of block rubber has been formed. It should only be necessary to point out that essentially block rubber is merely pressed crepe rubber. It is inconceivable that the mere action of pressing layers of crepe together would increase the physical quality of the rubber.
The advantages which block rubber possesses are the compactness of the output, its ease of packing, and a saving in freight; but there is the disadvantage, from the consumer’s point of view, that extra labour is involved in the preparatory work of cutting up the blocks.
Smoked Crepe and Sheet Clippings.—There appears to be no certain demand for any grade of smoked crepe, and probably all which is put into the market is really comprised of (1) clippings obtained from the ends of sheets, (2) sheets which have been malformed in machining, or (3) sheets showing the presence of many “bubbles.”
As to the first class it might be explained that through defective rolling, thick ends or edges may be caused. These show signs of contained moisture when the bulk of the sheet is perfectly dry, and as undue delay would otherwise result these moist strips are trimmed and either returned to the smoke-house, or machined to form crepe.
Similarly a torn or otherwise badly formed sheet, when brought from the smoke-house, may be made into crepe, rather than it should prejudice the selling price of the bulk under ruling conditions.
In the same manner, although “bubbles” have no influence upon the quality of the rubber on vulcanisation, sheets thus affected are generally made into crepe.
It cannot possibly be argued that rubber of this description would be in any way inferior to the best smoked sheet for manufacturing purposes, but owing to the prevailing system of evaluation for market purposes, it is necessary to resort to the expedients indicated above.
On some estates the rubber specified in the three classes mentioned is not made into crepe, but cut up into small pieces and shipped as “sheet clippings” or “sheet trimmings”—a procedure which would appear to be justified by a steady demand. In point of fact, the buyers are really obtaining a first-class article (except in superficial appearance) at a reduced price.