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Identification of Plastics

Unless you have a mass spectrometer in your basement, identifying plastics requires a little background. Here are just a few rules:

  • if it floats in water, it is either polyethylene or polypropylene
  • if it has a metallic "clink" it's probably polystyrene
  • if you are willing to burn some of it with a soldering iron or match, you can get a lot of information. Texloc has a great chart covering most of the modern plastics and some of the vintage plastics.
The Smell Test

The most reliable way to distinguish vintage plastics, short of the mass spec, is by scent, but it takes a little experience. I will rub a piece firmly with my thumb to heat it until it emits an odor. Hot water works very well on buttons, bangles, etc, but use with caution on Mah Jong tiles – it can lift the paint. It’s a little harder to get a scent from casein – I have used very fine sandpaper (6000 grit) to heat it enough to smell it.

Bakelite and Catalin have a very distinctive smell – a sweet chemical odor. Once you smell it once or twice, you can recognize it easily. If you haven’t spent much time at the chemistry bench, find a piece that you know is bakelite, or confirm by other means (see below), and get familiar with the scent.

Celluloid is made with camphor, and will smell like mothballs or pine sap.

Casein is made with animal protein, and smells, unfortunately, like wet dog.

Lucite and Plexiglass are odorless.

Other Tests

On exposure to UV light, catalin and bakelite form a layer of phenyl alcohol. This is responsible for the change in their color with age. Learn more...Cleaners such as Simichrome polish, 409, or Scrubbing Bubbles will remove a bit of this phenyl alcohol, imparting a yellow tint to your cotton swab. This phenyl alcohol means that vintage bakelite is never white.

One foolproof way to identify celluloid is use of acetone. It will dissolve celluloid completely. I don't recommend this as a routine method of identification.

 

Visual Clues

Thin pieces of casein plastic develop a subtle crackle texture as they gradually lose moisture (fig 1). Celluloid can be almost white (but not quite). In game pieces it may be in french ivory form – darker and lighter sheets compressed together to imitate ivory (fig 2). When it discolors with age it can yellow or take on a pinkish brown tone. Catalin is variably translucent, and typically swirled (fig3). Later plastics imitated this look, but don't have the dense, almost stone-like feel of the phenolics.

casein chip french ivory catalin
Fig. 1 Old casein
Fig. 2 French ivory Mah Jong tile
Fig. 3 Catalin Mah Jong rack

 

 
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