Ivory
Closely scrutinize the surface using a magnifying glass or even a microscope. Ivory, bone, and plastic have unique characteristics which differentiate them from each other.
Ask the following questions:
Is the surface lined or smooth? Absolutely smooth surfaces are a characteristic of plastic.
If the surface is lined, do the lines (on any side) crosshatch or run generally parallel? Cross hatching (roughly diamond shaped cross hatching) is a good indication that the material is ivory, as are translucent wavy lines.
Roughly parallel lines are a good indication that the material is either cut lengthwise from ivory (older ivory is cross cut) or possibly bone.
Genuine Elephant Ivory will have the grain running roughly parallel, if the lines are perfectly parallel, odds are its imitation Ivory. Genuine Mastodon Ivory will have a lot of cross hatching, especially around the outer rim when looking at a cross section. Genuine Whale Ivory will appear much whiter and smoother than most other types of Ivory. Genuine Walrus Ivory will have heavy dark spots in various areas of the surface. The center of the fossilized Ivory will have marrow that is much tougher and harder to work than the outer layer.
Genuine Ivory is seldom "smooth" in its natural form. It must be polished smooth before it can be used for scrimshaw or carving. Some Ivories such as Mastodon will have an Outer Bark Layer often exhibiting fantastic shades of blues, greens, purples, browns, etc.
When purchasing scrimshawed or carved Ivory, look for small mistakes in the workmanship such as lines that have "moved" or re cut. This is a good indication of hand carving. A lot of "fake" pieces are drawn with tattoo needles and computerized equipment and some are even simply applied designs that will wash off under running water.
Does the surface have multiple darkened dots or pits? If so, this is a very good indicator of it's being bone. Ivory tends to be smoother, harder, and not pitted.
If the surface is smooth and you see no obvious lines, try heating the tip of a pin to red hot and touching it to the surface of the object in an area that is not easily visible. If the hot pin dents the surface, you've got a plastic object.
Feel around the edges, bottom, and top for a single line. If there's a line that sticks out and continues all around until it meets, it's plastic — the line is from when the two molds containing the plastic are put together, fusing the two halves together.
Keep in mind, plastic is usually very easy to tell from ivory and bone, as it is generally lighter (in color and weight) than ivory or bone. Also, the color is even and consistent all over.
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