Use your hand and touch a gold leaf. If it is gold 999/1000, it will suck/adjoin at your skin and be difficult to peel off again. Gold on base or Composition Gold can be handled easier and be taken off very easy.
If you pulverize a gold leaf between your fingers the gold 999/1000 will stick and slowly permeate and leave just a little gold shimmer in the lines of your skin - gold on base and/or composition gold will break into small pieces and will not disappear.
Put a drop of Nitric acid on your gold material and wait 30 min - 1 hr. If the material disappears, it is not gold 999/1000. If the acid doesn't destroy the material, its gold 999/1000. If the material turns red then it is a lower karat gold. Pure gold will not vanish.
If you heat or burn gold 999/1000 it will melt into a small nugget.