Damage from contact with mercury, caused for instance by the accidental breaking of a thermometer, is the most severe damage a jewel may suffer – and, unfortunately, in most cases it is irreversible.
Mercury creates an amalgam with gold, and often jewels cannot be repaired. In order to restore the original state of a jewel, as a first step it is fundamental to remove mercury. This can be done only with a high-temperature process which is highly toxic, since mercury vapours are extremely toxic. At the end of the treatment the jewel surface becomes extremely porous, making it unlikely for the original appearance of the jewel to be restored. Moreover, the colour of the alloy will differ from the initial one, since it is very difficult to remove mercury completely.