Question How do you un-equivically determine if a stamp is the "blueish-paper" (35% PULP) stamp? I have one without watermark, whose perfs put in as a contender...but it doesn't look particularily blue.
Answer If it has no watermark, it can not be the real bluish paper (which is actually gray, not blue) because no unwatermarked stamp was ever issued on bluish paper. I always recommend to collectors that to learn how to correctly ID bluish paper, spend the money to purchase one that comes with a recent expert service certificate, then use that stamp as your reference copy. A Scott #357 or #358 with small faults can be purchased for under half Scott value and at that price, it's a bargain to help you learn how to correctly ID bluish paper. Hope this helps.