Everything metal in your garage is in danger of oxidation even the metal not in your designated spot.
When gold is (oxidized) (loss of electrons) we say it is dissolved into solution, the acid is reduced (gain of electrons from gold), reducing the gold (gain of electrons) each gold ion becomes a metal atom with a full shell of electrons, these gold atoms join together to form a heavy enough particle or cluster of atoms for us to see and to overcome the gravity in solution to precipitate.
Gold can colloid, here the reduced gold clusters of atoms do not grow large enough for us to see, the cluster of gold atoms here will not become large enough to precipitate, in fact, they become electrically charged of different polarities and repel each other in solution, this repulsion of clusters stops them from joining and can keep the reduced gold in solution (even after hundreds of years), you cannot precipitate it, you cannot test for it in solution, because this gold is already reduced and cannot be reduced with our testing reagents, or with any of our reducing agents...
How big the cluster of gold atoms gets is what gives different colors to the solution or different colors of colloidal gold solutions.
Colloids give the Tyndall effect with a flashlight.
Gold can precipitate at different colors, normally black when impure to a light tan brown when the precipitate gold is purer. I have seen several times when gold will precipitate as small gold color powders, much more gold atoms and more bonded together...