"gods of silver": What is the intent of this? Is it not already written "gods of gold"? Why, then, add "gods of silver"? Because we find with all the implements of the Temple, if there is no gold they are to be made of silver, the same obtains with the cherubs, it is, therefore, written "gods of silver" — If gold is not used, they are considered "gods of silver."
What Does the Additional Prohibition Against God's of Silver Teach
Mekhilta Tractate Bachodesh 10:15