I have two pads of 140 pound (300 gsm) watercolor paper. One pad has a label saying it is acid-free and made of 100 percent cotton. The other pad also says it is acid-free but does not say what it is made of. Is there a simple test to know if paper is made of wood pulp or cotton?
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$\begingroup$ I wouldn’t say I’m a trustworthy source but from what I’ve found if you do a wet wash on a sheet of paper from each wood pulp paper will sometimes cause the pigment to be pushed to the edge creating a hard outlined edge. It’s worth a try $\endgroup$– Cam RienstraCommented Dec 4 at 16:28
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2$\begingroup$ One of possibilities is visual microscopic fibre comparison with known wood and cotton paper samples. $\endgroup$– PoutnikCommented Dec 4 at 18:15
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1 Answer
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Papers from wood (like the one for the Xerox, or desktop printer) usually contain starch. Papers from cotton (like the ones modern paper bills are made) usually do not.
Starch and iodine form a deep blue colored complex; so much so that it can be used to quickly identify counterfeit bills out of a desktop printer/xerox by help of a special pen. You can see them in use by supermarkets and alike because it doesn't require a / an additional power plug to run a black light lamp to see the marks of UV-ink (like the ones in your passport) next to the cash register. Though some shops equally have this little box aside, too.
(image credit www.safescan.com)
It might be worth check this option in a corner of the sheet. At time of writing the answer, this company (no particular endorsement for this one) sells them for less than $US 2 per piece.
(Of course, the paper's chemistry as such isn't the only safety feature to check a bill.)
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1$\begingroup$ Note that many banknotes - not necessarily US ones - are made from [plastic fibers](en.wikipedia.org/wiki/Banknote#Polymer_banknotes. Also in main article Polymer_banknote $\endgroup$– PoutnikCommented Dec 4 at 18:13
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1$\begingroup$ Yes of course (there already was a paper in paper bills, now highlighted more). And yes (one of the forerunners was Australia). $\endgroup$ Commented Dec 4 at 18:35
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$\begingroup$ Starch is internationally added to paper of various fibers for various purposes, called sizing, sciencedirect.com/topics/engineering/sizing-surface, and is particularly important for printer paper, to reduce linting and increase stiffness. It is no indication of the source of the fiber. $\endgroup$ Commented Dec 4 at 23:02