Examine the piece with a magnifying glass. Plastic items will be smooth. Natural materials such as ivory and horn have a grain.
Consider the color and condition of the piece. Ivory turns yellow with age. Additionally, uncared-for ivory may develop cracks and other defects due to age.
Write out the item's history as you understand it. The age and origin of the piece will aid your later comparisons.
List the defining features of the piece such as its size, shape, any remaining natural features and the subjects of the carving or engraving. Whaling scenes are the most commonly collected, but other nautical, home and patriotic scenes are also valuable.
Examine any signatures, artist marks or dates. Not all scrimshaw have these additions, but the most valuable pieces are engraved with one or all. These marks will also aid identification of the piece.
Search public auction web sites for like pieces. This is the easiest way to gather additional information about your pieces. You can search for multiple known factors such as age, origin, material, scene and/or artist. A systematic search could begin by searching with as many keywords as possible and then slowly expanding the results by removing key words. A search for "scrimshaw whaling scene" will return more results than "1821 scrimshaw whaling scene."
Buy a book about scrimshaw. This is a good second step if you have multiple, and possibly valuable, scrimshaw.
Consult an expert in American art if the piece's provenance or the previous search results lead you to believe your scrimshaw is valuable; was made of whale ivory; or from before 1910. If you plan to sell the piece, an art auction house will necessarily authenticate your scrimshaw. Many large American cities also have art appraisers that can authenticate scrimshaw for a fee. Conversely, a local art museum or university art department might be willing to examine your heirloom scrimshaw for free.