I must point out that the way Viserys was executed ignores real physics: the hottest a typical campfire gets is maybe 600 degrees F. In order to melt gold, a fire needs to reach 1947 degrees....
for historical reference, a roman named Marcus Licinius Crassus (wealthiest Roman in the historical record, worth some 200 BILLION dollars in today money) was said to have been executed after having marched into Parthia in an attempt to seize MORE gold and presiding over one of Rome's greatest defeats at the battel of Carrhae by having molten gold poured down his throat by his Parthian captors. I'm guessing GRRM took some inspiration from that historical tidbit.