Besides the fibres, pulps may contain fillers such as chalk or china clay, which improve its characteristics for printing or writing. Additives for sizing purposes may be mixed with it and/or applied to the paper web later in the manufacturing process; the purpose of such sizing is to establish the correct level of surface absorbency to suit ink or paint.
When are additives for pulp purposes mixed? (If the question is unanswerable, say "unanswerable")
unanswerable