China Clay paper

China Clay paper was once considered a major paper variety for US Washington-Franklin flat plate stamps.

It was first used to describe light-colored paper thought to have kaolin/clay added. It was then taken to mean a somewhat grayish paper different from that found in the bluish paper issue. For one, the bluish paper stamp paper has a high quality rag/cotton fiber content so that when held to the light, the double line watermark is clearly seen. This is not so for "standard" double line watermarked Washington-Franklins included the so-called China Clay types.

China Clay paper became a sought-after "type" at some point, gained Scott catalog listings and were certified by expert groups. Eventually, proper chemical analysis showed that China clay papers did have a slightly higher silica content thought to be due from dirtier water used in the papermaking process. And nothing more. So, this was a very minor paper variety and not a major one, and was de-listed from Scott. A current term for China Clay paper is dirty water paper.

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