We can infer from the passage that before bleaching was discovered, ……………

Paper-making technology improved rapidly throughout the 19th century. The introduction of chlorine for bleaching meant that white paper could now be manufactured from coloured linen and cotton rags, thus increasing the range of available raw materials. Even so as the century progressed, the demand for paper increased dramatically, and other sources were sought. Esparto grass from Spain and North Africa became a valued commodity for paper-making. Only when it was realized that wood pulp could be used as a source, however, did large scale paper manufacture become possible.