In this episode Terenzio and Sinfosio talk about metal oxidation and how to clean coins with acids
In the municipal villa, 2.30 pm
Terenzio and Sinfosio meet
Terenzio << Good afternoon, Master Sinfosio >>
Sinfosio << Good afternoon to you, Terenzio >>
T << I have good news for you, do you remember that job offer that I mentioned to you last month? >>
S << Of course, Terence. The new workshop on the outskirts of the city was looking for an assistant-boy and you submitted your application for that position >>
T << Exactly. Well, a few days later I got called and they immediately offered me the job. And you know the amazing thing? They pay in advance! >>
S << Eureka! Dear Terenzio, consider yourself a lucky man: you will be able to give away your basic income and finally be a gutsy man >>
T << This flatters me, Master >>
S << May I then offer you a warm chicory-based drink? >>
T << Of course, gladly! >>.
While they are sipping their drinks…
T << Do you know a little something about what happened to me a few days ago? I had my weekly wages in my pocket, precisely 7 copper axes and 2 gold aurei, and I was intent on preparing my famous peppers in vinegar when all the coins inadvertently fell into the goatskin full of vinegar. I did not notice this; in fact, I finished the job and went out. And you can imagine the discomfort when I realized the loss of my coins: I was looking everywhere, but nothing… they were like evaporated! >>
S << You must be more careful, my dear Terenzio. It was also your first salary>>
T << I know it well, master! Anyway, my wife cooked the peppers yesterday and she did notice the coins only at the end: she prepared a nice saucer full of eggs and peppers, with a final sprinkle of metal disks! What a laugh! >>
S << I must say that she prepared quite a rich dish >>
T << Sure. And you know what? The gold coins were unchanged, but the copper coins were shiny, like new, bright… they looked like they were freshly minted. That’s weird! >>
S << Nothing new, my dear Terenzio. Did you know that gold is a noble metal? >>
T << Of course I know, if I had more aurei, I would be a nobleman too! >>
S << Not in that way Terenzio, don’t be silly. I mean that gold is a noble metal that is resistant over time, it hardly tends to oxidize, for instance… >>
T << Ossi-fy ??? >>
S << It is just a term, Terence! And it has nothing to do with bones, but with oxygen which is a powerful oxidant. Let’s say that most metals tend to react with oxygen to form an oxide. Many metals do this and thus tend to transform into oxides that have a lower value. While gold doesn’t! >>
Terenzio thinks about that for a while…
T << Oh yes! The aurei are always very shiny! While I have to say, copper axes tend to blacken. Will it therefore be because copper, unlike gold, ossif… ossifies? >>
S << Oxidizes Terenzio, O-X-I-D-I-Z-E-S. However, that is correct: copper reacts with oxygen in the air and tends to form a copper oxide layer which is a black solid. That’s why your axes turn black. But when you dropped them in the vinegar, they have gone back as good as new! >>
T << Oh yeah! But, why master? >>
S << Because vinegar contains an acid, acetic acid, which reacts with the black copper oxide layer, slowly dissolving it. Water and copper acetate are formed which remain in solution, while the copper of the coin which is intact under the oxide layer, gradually comes back to light and the coin looks brand-new >>
T << You master, you know many things. But isn’t the coin consumed in the end with this process? I mean copper is consumed over time, isn’t it? >>
S << Well, yes! Some of the coin gets worn out and if you repeat the process of blackening and acid-cleaning too many times, in the end, of your axes won’t be left an ASS! Anyway, Terenzio if you want to understand more about this phenomenon, my lab slave recently did an experiment for the children, let’s go to the lab so I’ll show you >>
T << Gladly master! This way? >>
S << No, over here. Follow me >>