America did not have a reliable source of domestic silver for their silversmiths to utilise during the 18th and early 19th centuries., and importing silver sheets from overseas was incredibly costly. They had to rely on melting down existing objects as well as coins to be able to produce their clients commissioned pieces. Due to the repurposing, grades of silver would vary during this time period but typically consist of 90% silver. Pieces during this period were stamped 'coin silver'.
Another thing to consider in the lead up to the revolution was the movement to boycott any British items due to the Stamp Tax.
It was not until the 1860's discovery of the Comstock Lode silver depository in Nevada and a mine was set up, that America had it first stable source of silver. The American Sterling grade was introduced in 1868.\
View items of coin silver currently instock here
(pictured are miners from the Comstock Lode mine)