An extremely rare 1812 legal tender "Joao VI Prince Regent" colonial gold ingot from Brazil has been sold for $199,750 (incl. buyer's premium) at Heritage's world and ancient coin auction at this year's Long Beach Coin Expo. What makes this particular ingot even more rare than its known contemporaries, is its large size (over 90 grams) and the fact that the accompanying assay certificate, know as a guia, is in outstanding condition. As Heritage states in the auction listing, the guia says:
"N.79. Deposited in this gold exchange house, Joao Baptista Maciel four ounces of gold from which the fifth for Royal Tax was paid and from the remainder a bar that weighed three ounces, one oitava and twelve grains. The Guia ends with "bar delivered at this Foundry of Sabara on January 7th, 1812."
In this case, the superb strikes on the ingot and the condition of the guia are the reasons this ingot sold for more than twice the price of comparable ones. Many surviving colonial Brazilian ingots have no guia, or a severely damaged one.
So, save that COA you get with your proof coins! Your great-great grandkids may appreciate it!