I have looked into the laws regarding silver tolerances around solder. It is a tolerance of 6 parts per thousand where solder is used and 2 where no solder is used. What exactly does this mean given silver solders are never plumb, most are around 60-70 percent silver which is around 400-300 parts per thousand non-silver metals. Does the tolerance mean the solder itself can only deviate by 6 parts per thousand or that the joint can only deviate by 6 parts per thousand? How would you know if you were safe or not?
Does this make fine silver with sterling as solder (which only deviates 75 parts per thousand compared to 400-300) safer than sterling and standard solder?
I am sort of confused and don’t want to break the law or sell something unethical so if someone could help me understand what these laws mean (or point me to someone who can) I would greatly appreciate it.