Silver has always been a form of money in the world, until currencies started coming into play. Historically, silver trades at about 12 ounces to 1 ounce of gold. Its currently trading at 60 ounces to 1 ounce of gold. I believe that main reason for this is because of the limited supply of gold in the world right now. More than 95% of all gold ever mined are closely held in the United States. Wile silver supply is dwindling, less than 5% of gold are circulating in the world today. Based on supply and demand, price of gold had traded at a very high ratio to price of silver.
Currently, the supply of silver is at an all time low, and the amount of silver circulating in the world are on par level as gold currently. That being said, would silver regain some grounds against gold when the supply goes down enough? I'm sure it would, the only thing is when.