GENEVA - In a Swiss workshop, eight skilled craftspeople labour to transform a very big block of crystal and some ethically sourced gold into the world's most sought-after cinematic award.

The Palme d'Or, a golden palm tree branch on a crystal base, is the top prize at next month's prestigious Cannes Film Festival and has been made by the same jewellers, Chopard, for the last 21 years.

The design has been tweaked down the years. After it is decided, a blue wax Palme is created and buried in plaster. It is heated in a furnace overnight to melt the wax away and leave a hollow plaster mould.

The 2018 edition is made from 118 grams (4.16 oz) of 18-carat yellow gold. The molten metal is poured into the mould, which is then dipped in cold water to break the plaster and leave behind a golden Palme.

Extensive sanding, cleaning and polishing take place before the Palme is deemed fit to sit on the crystal base created by stonemasons.

"We really wanted this Palme, apart from being a simple trophy, to represent the savoir-faire of different craftsmen," Marc Couttet, director of Chopard, told Reuters.

Two trophies are made, in case there are two top prizewinners at the May 8-19 festival. Five smaller ones have also been commissioned this year for other categories.

(Reporting by Denis Balibouse and Cecile Mantovani; Editing by Patrick Johnston and Andrew Roche) ((patrick.johnston@thomsonreuters.com; +44 207 542 9558; Reuters Messaging: patrick.johnston.reuters.com@reuters.net.))