Correct answer: 1. Museums replicate precious metal objects through electroplating, a technique in which metals are deposited onto a surface through electrolysis.
Some metal objects – such as coins, medals, busts and sculpted plaques – are so valuable that museums prefer not to put them on display. Instead they may opt to show copies of the pieces, but these replicas have to be accurate enough to fool the most discerning onlooker. The museums’ preferred method of copying is electroplating, which is the process of depositing a metal layer on a surface by electrolysis. When that electrode is a mold – as in the case of museum copies – the technique is referred to as electroforming.
“To start with, a metal salt is dissolved in a solution, usually water,” says microengineering specialist Grégoire Genolet. “By applying electricity to two electrodes in the solution, we can send a current through the solution. This leads to an electrochemical oxidation-reduction reaction in the electrodes: the metal in the anode oxidizes and ends up in the solution, while the dissolved metal at the cathode end reduces – by taking on electrons – and forms a layer on the cathode.” The metal layers build up on the cathode, atom by atom. And if the cathode is actually a mold of a museum piece, you end up with an exact replica. A better copy cannot be had.
Electroplating serves to create solid metal objects. But it can also be used for surface treatments in order to decorate or protect an object with a thin layer of metal on its outer surface, or to take an object’s imprint.
An age-old process
Electroplating is not a new discovery. It was the subject of a publication by Russian physicist Boris Jacobi already in 1837. One famous example of an object copied with this technique is the Gates of Paradise in the Baptistery of Saint John in Florence, Italy. In 1990, an electroformed copy replaced the original gates, which went into safekeeping. The gates are 5.21 meters high, 3.21 meters wide and 11 centimeters thick. That adds up to a whopping eight tons of bronze and gold.
Caption: The Gates of Paradise at the Baptistery of Saint John in Florence.
A modern process as well
Electroplating is not the sole preserve of the art world. If you look around, you will surely lay your eyes on an electroplated object. Pens, paperclips, jewelry, razors, eyeglasses, faucets – the technique is ubiquitous. Why is it so useful? “It is a highly precise way of producing objects with complex shapes,” says Jean-Claude Puippe, an electrochemical engineer. “Electroplating is a common component of cutting-edge technologies. For example, it has applications in medicine – for dental restoration and precision tool components – and it can be used in aerospace and experimental physics and to make watch movements.”
Grégoire Genolet is head of R&D at Mimotec, an EPFL spin-off that designs micromechanical parts using UV-LIGA technology (a combination of photolithography and electroforming).
Jean-Claude Puippe is a recognized electroforming expert and member of the board of directors of Steiger Galvanotechnique SA, a company that specializes in surface treatments using electroplating and electroforming.