First I Have Seen These: Terracotta Coin Molds From 310 Ad Alexandria:

I'm surprised that they have lasted so long with crumbling to dust. I have no idea what they are worth, these are the first I've seen outside of a museum so I imagine they very rare.

Those are pretty cool @lks! I've seen ancient Chinese coin molds, but not ones for the Romans.

A number of coins could be produced from one pour by keying and stacking the molds. It's likely than the metal for counterfeit Tetrarchic folles came largely from official coins with the silver content first removed by cuppellation. The silver thus recovered was the counterfeiter's profit margin. Any bronze or pot-metal scrap at hand to add to the crucible would be a bonus. The illustration below shows 3rd-century molds for denarii based on British finds but the functional setup would have been similar a century later.

I don't think the molds would have been used more than once. They are almost always found broken. Clay is (literally) "dirt" cheap and durable enough for a single use once fired into pottery. It is also brittle, making it rather easy to retrieve the finished product.