Gem and Ornamental

F I 2.6 Jet simuht showing uneven colour.The following are dl man-made polymers that were used in the earlyto mid-twentieth century, and resemble jet. They may be encounteredin the antiques world today. They also appear in Chapter 13 ('Plastics')where they are dealt with in more detail.Vuleanite is by far the most common of the jet simulants. It is alsoImown as 'ebonite' and is regarded as an early plasric. It was madeby vulcanising rubber, that is to say by heating rubber with sulphur.It could be mdded and mass produced and was therefore muchcheaper than jet. It was totally opaque and oolour was added tomake it a deep black. The colwr faded with age and today mostpieces display a greenib-brom hue (Fig. 2.3). They have dso losttheir high polish. Under magnifmtion tiny spots of wying colourmay be seen, a~ am a slightly pitted surface (Fii. 2.6). Vulcmitedid not split when worked so items of jdery could be screwedtogether (Fig. 2.1 1). The material was not completely rigid and, inthe case of necklaces, the links could be bent open to be joined(Fii. 2.9). Like jet, it gives a brown streak.Gutta pereha in its pure form is white, and in crude form can bebrown or black. It has the same chemical formula as rubber but adifferent physical state. It was not vulcanid as it was far toovaluable a material and was prized for its elasticity and plasticity,and would have been ruined by vulc~tion, It was my easy tomould and could take intricate patterns, but to be made intojewellery, it would have needed to be hardened in some way. Gumper& was less durable than vulcanite, and cmcked and deterioratedwhen exposed to air over a long period of time. Instead it kept