I get 13.
Take one coin of each chest.
a) You get two Gold, one Silver:
Silver is identified, remains to distinguish all_Gold and Gold_Silver.
Take 10 more coins from the first G:
- if they are all gold, you identified all_Gold, the remaining is Gold_Silver
- if you get a silver coin, you identified Gold_Silver, the remaining is all_Gold
b) You get one Gold, two Silver:
Same proceeding, permute Gold/Silver.