If the paper is thin, slick, or shiny, you likely have a reproduction.Under magnification, original paper will often show fluffy cotton fibers or, in later prints, even small splinters of wood pulp.
Measurements may be off slightly (usually smaller) due to changes over time, primarily from atmospheric conditions.
However, a difference of more than 3/8" in the longest measurement of a small folio (a bit more in larger prints) raises an alarm.
The best way to acquire a "feel" for the paper is to handle originals.
Lacking that, keep in mind that modern paper is noticeably different from the old rag paper.
Conningham" is the preferred collector's reference, and a must-have if you're going to be buying, selling or collecting Currier & Ives lithographs.
You'll know it's not authentic if you see the name of any other printer or publisher (often with a modern copyright � symbol), or an address other than New York, a 20th century date, or words such as reprinted from, republished by, from the collection of, courtesy of, or from (or after) an original by.
(If the print is still in the original frame, you may find a Max Williams label). Lipshitz or Joseph Koehler are easier to pick out, generally carrying the new publisher's name. they're a highly reproduced series.) The better reprints can be "foolers," particularly large folio copies that are partly hand-colored, heightened with gum arabic, and "the right size." They may be old enough to show age toning, or reproduced by the collotype process, which doesn't give telltale symmetrical dots.
Some of these reproductions, such as the 1942 Andres prints, originally carried a printer's identification at the bottom edge which frequently has succumbed to scissors.
The good news for collectors is that most reproductions are not that hard to identify.
Here is what you should look for: Read the small print.
On a Currier & Ives original you will generally find: For some of the following steps you'll need a reference book.