Bakelite and red coral are two popular materials used in vintage jewellery pieces. Bakelite is a thermoset plastic, while coral is a natural material. The smooth and shiny coral found in jewellery is typically not grown in reefs, but is the calcified remains of a marine animal. There are several tests that can be performed to determine if an item is red coral or Bakelite. They are organised from the least harmful and most simplistic to those that could cause damage if assumption of material is incorrect.
Analyse the colour of the piece. Red coral will appear in shades from deep red to light pink. Bakelite was produced in red as well as pink. However, authentic pink Bakelite acquires an orange patina. The hue of red coral and red Bakelite do not degenerate.
Click to together two pieces of the same material. Bakelite, lightly struck with other Bakelite, will produce a distinct clinking tone.
Pour a glass of milk. Place the suspected coral in the glass and watch the milk turn pink. If the milk remains white, the piece is not coral or it has been lacquered.
Place the jewellery in a glass of vinegar, heavily diluted with water. If bubbles appear, the piece is coral. Calcium carbonate effervesces in acid.
Run the jewellery under hot running water. When removed, rub briskly with a finger. Fingers will smell like carbolic acid if the piece is Bakelite. There are some cases where this test creates a false negative based on colour. Different chemicals were used to make the array of colours.
Test the piece with simichrome if all prior tests do not clearly indicate material. Dab a small dot of simichrome polish on a clean cloth and wipe the palm side or reverse of the piece. If the cream on the sock turns amber yellow, the jewellery is made of Bakelite. The chemical reaction does not harm the jewellery as the chemical is reacting to the layer of patina and not Bakelite itself. As with the rub test, false negatives can occur. In this case, it is likely if the piece has been stripped or abrasively cleaned or restored.
Heat up a straight pin using boiling water or a match. A third Bakelite test, the most foolproof, involves poking an inconspicuous area with a hot pin. It is not recommended unless the possibilities of other materials have been eliminated, as it has the potential to cause damage. When a hot pin is pressed to Bakelite, it will not create a hole. Bakelite is fairly impervious to heat, making it ideal for television casings and automotive applications.
Seams do not appear in Bakelite or red coral. The 1930s and 1940s is considered the heyday for Bakelite jewellery, although there are modern versions produced. The most valuable coral displays the deepest shades of red. When in doubt, err on the side of caution. If the prospect of these tests create anxiety, consult an antique dealer or gemologist.
Examine the clasps, prongs and secondary stones in the jewellery. Rhinestones and fabric pieces may not withstand the suggested tests. Use prudence, remove the pieces prior to testing, or perform the least invasive tests.