Dark green, hard spots are usually OK but probably need to be monitored. Light green, powdery, flaky is bronze disease and should be treated if possible.
Looks like corrosion, not BD. I think the three coins are fourees, and the copper core is corroding in places. BD is like a fungus, and it will grow larger over time. If it doesn't grow out of the coin and appear bigger after a week or so, it's probably not BD. If it doesn't brush off easily, it's probably just corrosion. Corrosion is very common on ancient coins. BD is not. So for now, just keep an eye on all the coins. Check them regularly for a month or so. If the green isn't growing, it's not BD.
They look like fourees of Baktrian drachms. Authentic drachms would be solid silver, not billon. These coins look like they have a copper core covered with a thin sheet of silver. But I'm just going by the photo. They may look different in hand.
These are I do-Scythian tetradrachms. They are very large coins, and are billion. These are my first billon coins, so I’m not sure if they would have any copper coloration. Should I shaft a new forum topic on this?
You will get responses from people much more knowledgeable about Indo-Scythian tetradrachms than I am if you start a new topic with that header.
