This is an excerpt from an essay I posted in 2003 at my Yahoo Group, Amber Forever, in the Files Area, titled "Testing Amber"—and available as a PDF:

"The problem with "aroma tests" is that they demand some sort of
characterization that is usually personal/experiential and comparative. Taste is
made is from combinations of sweet, salty, bitter, and sour. Smell, on the other
hand, is infinitely more varied—well beyond any standard language or terms to
describe any particular aromas. So, we compare one thing to another—and what
this communicates might be meaningful or meaningless. Plus, frankly, lots of
people do not seem to have very good senses of smell. I meet people often who
demonstrate no confidence or ability to make smell comparisons or
characterizations.

The required tools for the hot-point test are a long, thin steel darning needle and
a candle. The steel needle is important, because something like a paperclip or a
length of wire will not stay hot enough long enough to do the job. A shorter or
smaller needle will become too hot to hold comfortably. If a long needle isn’t
available, a shorter, smaller needle will do if you place the eye-end into a piece of
cork. This allows you to hold the needle without burning your fingers. A lit
candle is preferred for the source of heat, rather than trying to light matches or
a lighter, because it frees your hands to hold the needle and the specimen. (Once
you’ve used a needle for a hot-point test, it’s no longer a very good sewing needle.
Place it aside for later, further tests.)

By the way, I always warn people to use real caution in testing plastics with the
hot-point. Celluloid is highly inflammable, and can practically explode into
flame. Some plastics (i.e., polyvinyl chloride), when they are burning are quite
toxic (!!). I advise working in a room with good ventilation, and carefully
the aroma (not deeply inhaling it). I also recommend that one not
test too many items in one sitting, because the nose becomes overwhelmed, and
eventually everything smells "the same" (nasty). The tip of the needle should be
placed in the flame of the candle until it's red-hot, and then inserted into the
perforation of the bead (or applied at a discreet place, like the bottom or back),
and stroked a couple of times. Natural resins (like copal) and thermoplastics
melt easily, with characteristic aromas. Amber melts, but not easily—and like
copal makes a "pine-like" aroma. All thermoplastics melt to some degree, usually
easily, and some spin threads when the needle is withdrawn (which amber will
not). These each have their own characteristic smell. Old-time Celluloid
included camphor—which affects its aroma considerably, making it somewhat
resinous. Casein (Galalith or Erinoid, made from milk solids and formaldehyde)
may smell "fishy" when wet, but gives a smell like that of burning hair, with the
hot-point (and so does horn—another amber imitation—and other keratinaceous
materials). Acrylic (Plex, Plexiglass, or Lucite) makes a sweet ‘fruity” smell.
Some thermoplastics make a sicky-sweet smell. (I used to think this was
polystyrene, but now doubt this. However, whatever it is, some people think the
smell is “resinous,” although I would tend to disagree.) A "smell-less" plastic
should be hot-point tested. It will make a smell. The odor of Bakelite and other
phenolic plastics is that of carbolic acid. This characterization may be relatively
meaningless to many people. I advise folks to go into their kitchen, select a
Revere Ware pan—or any pan with typical black Bakelite handles—and to rub
and smell it for comparison. Thermosetting plastics will not melt, but will make
a distinctly unpleasant odor."