I am looking for a graph of at least a table with data that would allow me to make a graph, showing how the gold/silver content was slowly removed from roman coins due to debasement of the currency.
The data is from Walker, D.R. (1976-78), The Metrology of the Roman Silver Coinage, parts I and III.
There are usually a few things to consider with data from so far back. In this particular case,
- the data is for the denarius and the antoninianus, and hence exclude the quinarius and eastern provincial coinage (drachma, cistophorus, etc.)
- before the civil war of 69, the exact time of a coin's manufacture within a reign is usually unknown
- according to Butcher and Ponting (2009, "The Silver Coinage of Roman Syria Under the Julio-Claudian Emperors"), Walker's data, which relied on scratching the surface of a coin, can overestimate the silver content because surfaces had been deliberately depleted of their copper content at the time of manufacture, and further depleted by natural processes during centuries of burial and the processes of cleaning after their discovery.
The paper of Butcher and Pointing also has plenty of data (presumably more reliable) and plots.