Were Severus II radiates silvered?

[Romulus17]

I've posted this question on the Forum board but thought I'd ask here as well.  I know the folles were originally silver washed but were the radiates?  If so does anyone have an example?  I know they would have to be in top condition and expensive but not as expensive as the argentei.  Thanks

[Peckris]

It's said that radiates were very similar to the antoninianus, but had "little or no silver".

[NumisDom]

Yep, I've not seen a washed one.  

[pokal02]

I'm fairly new to Roman and for now am concentrating on London Mint issues - Spink describes them as 'billon' up to Maximian & 'AE' thereafter.  I've seen various items described as 'billon', copper' and bronze in dealers lists.  It's my understanding that all the London Mint folles/nummi/'AE3's contained some silver, starting with about 4% and gradually reducing to nearer 2% - is this correct?  (The later coins of Constantine I/Crispus seem to turn up silvered more often).  Does a coin need a certain amount of silver to be described as billon rather than bronze, or are some dealers just deciding that if a coin looks bronze/copper they'll describe it that way?  .