This is a lost art and a lost part of english history..the phrase "Essex Crystal" has nothing to do with the Towie luckily , and though probably mis-named is called after William Essex, an artist well known for his miniature enamel work in the C19th.  The technique is actually reverse Intaglio carving & painting, carving into glass or rock crystal panels and filling in with paint and then stone settingthe glass in gold or silver mounts. It became very popular in the mid C19th ,and was perfect to portray hidden messages from flowers albeit with little intrinsic cost  . Once machine stamping made mass production of jewellery easier, this complex technique died out..Pieces today are hard to find, naturalistic subjects include animals, flowers and plants , viewed front on the jewels sparkle and the cabochon glass magnifies delicate painting ....