Inclusion

An inclusion is a tiny piece of foreign material that was in the wood pulp slurry used to make paper. So, it is throughly imbedded in the paper and cannot be removed – don't even try.

It could be any impurity, even a tiny insect, but this is most commonly a dark bit of tree bark that could not be bleached out in the papermaking process. It is disfiguring to some degree and will affect the grading of very high quality stamps. Otherwise, it could be something to avoid when buying stamps or just something to live with. Then again, if you always resort to very high magnification and look hard enough, you will always find inclusions and flaws in wood pulp paper – you will never buy a single older stamp. Plus, there are issues that are never free of impurities like the French GC paper of the early 19th Century. So, inclusions of one kind or another are sometimes a key to confirming certain issues.

Be aware that one or two tiny pieces of hairlike threads does not make granite paper. They are accidental inclusions.

 File:Inclusion.jpg|Two different types of inclusion, one at the two o'clock position in the margin, one around the five o'clock position. 

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