gold deposited from amalgam

In _Electro-Deposition_ by Alexander Watt, 3rd edition, page 202, it says:
"Mercury-gilding, formerly called wash-gilding, water-gilding,
or amalgam-gilding, essentially consists in brushing over the surface of silver, copper, bronze, or brass an amalgam of gold and quicksilver, and afterwards volatilizing the mercury by heat. By repeated applications of the amalgam and evaporation of the mercury, a coating of gold of any desired thickness may be obtained, and when properly carried out the gilding by this method is of a far more durable character than that obtained by any other means."
Why would that be? Why would gold deposited from amalgam be more durable than electrodeposited gold? What differences would there be in the grain structure of mercury-gilded gold as compared to electrodeposited gold?
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