To my knowledge, denarii do not have the lunar symbol below the bust, or sometimes with just the ends in front of the shoulders. That’s what I’m seeing here, but it’s labeled a billon denarius instead of a antoninianus. The reverse type is for both denominations, unfortunately. Do you agree with their label, or was it supposed to be a antoninianus?
Yeah, I forgot that’s their typical title for an antoninianus. So a mislabel then, still. “Bl” is short for billon rather than the word double
Because speculators think that if they throw any ancient scrap of metal into a slab, some fool will come along and be parted from his money. Unfortunately, they're right.
Here's my Salonina, which is labeled as "BI Double Denarius". Kind of tough to make out the details on yours, but it looks like the same type to me. I think you might be on to something, but then again, I'm no expert and I'm not aware of all the nuanced determinations when it comes to these things. I do not ever recall seeing a coin labeled "BI Denarius" or what that label would even refer to as a denomination, so I'm guessing that @Victor_Clark 's suggestion is probably correct "Meant Double".
Billon is any alloy where the base metal is a larger percentage than the silver, 51% and up. Salonina's antoniniani are definitely billon, even though they frequently look somewhat silvery. It's surprising how little silver you need to add to copper to make it look silvery. Plus, the Romans had techniques for coating base metal coins with a thin layer of bright alloy (usually some combination of zinc, antimony, and lead). Those coins are said to be "silvered."
This Salonina I have is 54.75% silver. The one below only 31.66%. The silver content during this reign varies wildly and not always in a linear fashion. It's as if they got by on what they had at hand. Rasiel
