Sentence:  Any power rail needs to be well insulated from earth, to minimise current leakage, and so the "two" power rails on the Underground sit on curiously genteel and antique-looking <WSD>porcelain</WSD> pots. 
Meaning of the word marked with <WSD> tags:  A hard white translucent ceramic, originally made by firing kaolin, quartz, and feldspar at high temperatures but now also inclusive of similar artificial materials; also often  such a material as a symbol of the fragility, elegance, etc. traditionally associated with porcelain goods.