Rich,
Some real ivory has grain that is very difficult to see with the unassisted eye, a 15-20x loupe is a tremendous help - celluloid/Bakelite does not tend to get check-cracks that are long, normally they'll be short (0.150" or less) and erratic whereas bone & ivory . Depending on the storage/use conditions Bakelite/celluloid may not produce a readily detectable "old Lionel xfmr smell" (excellent analogy Nate) with the finger-rub test. You can also do the "feel" test, at room temperature, ivory will feel cool to the touch and plastic will feet warm.
Don't be quick to toss something that is plastic because depending on the item and sometimes the specific type of plastic, it may actually be worth more than it was real ivory.
Here's some info from a website:
>How do I tell if something is ivory, bone or an ivory substitute (plastic or resin)?
Ivory is actually the natural tooth of an animal. Teeth continue to grow throughout an animal's lifetime and as a result, they have a noticeable structure and "growth lines" (called Schreger lines in elephant ivory). Look at the piece carefully under a magnifying glass. Under a 10x magnifier, elephant and mammoth ivory will have visible striations or grain that often show up as diamond or "V" shapes or cross-hatching on the surface or edges of polished ivory. Bone lacks such "V" shaped striations. Under magnification bone usually shows minuscule circular or oval shaped dots on cut surfaces. These dots are the tiny vessels that once supplied the living bone. Also, bone exhibits grain-like parallel striations and usually has dark flecks of dirt particles caught in the pores of cut bone -- all not present in ivory. Resins or plastics have a uniform surface, usually with no striations or diamond or "V" patterns, however some manufacturers are now introducing faux ivory with an attempt to reproduce some of these features.
When looking at a piece, check the bottom or sides for the diamond or cross-hatch pattern typical of real ivory. Then check again for a slight wood-grain pattern, this is also typical of real ivory. Next, check the feel. Real ivory should have a cool-to-the-touch feeling. Resins or plastics may duplicate one or some of these features, but none duplicates them all.
Also, color often varies slightly (I emphasize slightly) throughout natural ivory (more variable in mammoth) from a creamy white to a creamy yellow-tan or a creamy, light yellow-brown, whereas bone and plastics are either consistent in color throughout, or their color variations may be extreme, especially in stained or colorized resins and plastics.
The next test involves using an inexpensive blacklight which you can find at most department or home improvement stores. Shine the blacklight on the piece. Ivory develops a beautiful natural patina with age which shows up as a yellow-brown overall color under normal lighting conditions. Under ultraviolet light, where the original ivory surface shows through the patina, the ivory will show up a bright white. When ultraviolet light is shined on resin or plastic ivory substitutes, the ultraviolet light is absorbed and they exhibit a dull appearance. (The light emitted by many long wave ultraviolet radiation lamps is hazardous to the eyes. NEVER look directly at a UV light.)
You can also take a Q-tip, dip it in alcohol and rub the piece in an inconspicuous area. If the patina comes off and colors the Q-tip, chances are good it's a paint or varnish or some other substance that was applied to give the impression of age.
There is one other way to tell if a piece is ivory or plastic, but be aware this should be used only as a last resort since it can be a destructive test, especially to plastic. It is the "so-called" red hot pin test. Take a pin and heat it in a flame until it is red hot. Touch the hot pin to an inconspicuous area of the piece. If it is real ivory, nothing much will happen. It may, however, produce a tiny smooth scorched point (which is never good for the resale value of a genuine ivory piece). If, on the other hand, it is resin or plastic, the needle may melt into the surface and produce a "burr" or small rough spot (never something a seller of fakes is actually going to allow you to do). If you are very close when you touch the pin to the piece, what you will notice most is the smell of burning plastic. The "hot pin test" is actually more myth than practical. No seller is going to let you touch a hot piece of metal to real ivory and a fraud won't let you do it to their plastic piece either.
The "hot pin test" results are actually very difficult to verify and again, let's face it, no seller is going to let you touch a hot piece of metal to real ivory and a fraud won't let you do it to their plastic piece either.
