Yes, this subject has been discussed before.
in those day's the value was the weight, a lump of gold/silver say 3.5 grams was the same value as a 3.5 gram coin
I don't think so. With a coin you can go off and buy a
pot of garum or something else. What can you do with a 3.5 gram lump of silver? Of course when the coinage was first established it was based on the perceived value of the metal, but then someone invented debasement.
As we all know, the amount of silver in the
denarius decreased over time, although the overall
weight remained roughly the same. However, the value of the
denarius also stayed the same. If it could buy two loaves of bread before debasement, it could buy two loaves after. There was no point in debasement if this was not so.
Debasing the silver coinage effectively increased the
price of bullion silver (in terms of
denarii) since if you took a lump of silver bullion to the
mint (assuming you could) you would receive more
denarii than you would have done before a debasement.
The point about coins is that you didn't have to know exactly how much they weighed or what their metal content was. Indeed there was no way of measuring this in every day transactions. You just
had to 'believe'. So the
weight or composition of a 'forgery' was not easily known. The design on the faces of them might more easily be seen but mixed up in loose change, who knows?