Chimneys only work because hot air rises, which it does for reasons that I’m sure I’ll explain in more detail someday. But today is not that day. For now, we can just content ourselves with that statement and move on: Hot air rises. That’s not where my interest here lies, anyway. My interest lies at the bottom of the chimney. The fire in a fireplace can get pretty hot, anywhere from 500 to 1,100 or so degrees Fahrenheit. (That’s 260-600 Celsius, if you’re into that sort of thing.)
There’s a lot of complicated chemistry in a fire, but this is a physics blog. We can imagine the whole thing as reactions that combine oxygen from the air with carbon—making carbon dioxide—and hydrogen—making water—in the wood. Those reactions give off energy (loosely speaking), and that energy both sustains the fire and heats the surroundings. It can seem unbelievable at first that fires give off water, but you can prove it to yourself the same way Michael Faraday did: Put a piece of glass above a burning candle and, among the soot, you’ll see condensation. The soot is evidence of the chemistry I’m avoiding; the condensation is evidence of water.
Anyway, fireplace fires can be hot, but they’re nowhere near hot enough to melt most metals. Silverware used to be silver, sensibly enough, and silver melts at 1,700 degrees. Today’s utensils are often made of metals like aluminum instead of silver, but the melting point (and the broader point) is effectively the same. You’re not getting there in your home fireplace, no matter what kind of fancy system you’re running. Getting an oven that hot requires reinforcements. You often need to burn the remnants of ancient wood and other plant matter—what we’d more conventionally call coal. (Or propane. Or something else that burns that hot.) Once your oven is that hot, you’re able to melt all sorts of metals, pour them into molds, and form them into whatever shape you want.
The other option, of course, is to make your spoon out of something that melts at a low temperature, like gallium. Gallium spoons are a pretty popular gag among chemists, although it’s not an element you want sitting around at the bottom of your tea.