Philatelic Mixtures and Multimodal Densities

Abstract

Abstract A century ago, postage stamps were printed on a deliberate mixture of different paper types, each having its own thickness characteristics due to poor quality control in paper manufacture. It was not unusual for different types of paper to be used for a single stamp issue, because ordinary white wove paper was often not readily available in quantities necessary for production of a new stamp issue. Unfortunately, the different paper types used were not always well documented. Each paper type was purchased by the ream, which was required to consist of a specific number of sheets and had to weigh a certain amount. To cut costs, manufacturers often satisfied both requirements by mixing a few “thick” sheets of paper into an otherwise underweight ream. Although the importance of paper thickness in the philatelic literature is reflected by a higher market value for stamps printed on the thicker and more scarce paper, stamp catalogs have been notoriously vague about characterizing paper thickness, relyin...