In addition, recycled paper can be made into roofing felt or shredded into housing insulation. Paper cannot be continuously recycled because the fibers become shorter through the recycling process, eventually requiring replenishment with new resources. Not all paper is made with the same materials. If different papers or food-contaminated papers are mixed together, they contaminate the recycled paper, creating weak spots and areas of discoloration. Recycled pulp is blended with new raw materials to maintain quality.
Pulp is screened, rolled into new paper and sold to print shops and paper wholesalers.
To add gloss, shine, brightness or color to the paper, additives such as clay fillers, dyes and sizing are added. Papers with lignin are fairly inexpensive but have a disadvantage - the paper yellows over time. Office papers and magazines have had the natural lignin removed to maintain their whiteness. Early Europeans and Americans made paper almost exclusively from old rags. The paper mills could not find enough old rags to supply the huge demands for paper.