1. What happened to the container?
Do you know what material the container was made from?
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The container was made from 28 gauge (about 0.015 inch thick) mild steel with a 1-2 mil layer of tin electroplating on both sides. It was an oval can, 2 1/8" wide by 3 2/3" high and held 3 US fluid oz. Made by either the American Can Company of Chicago or Crown Cork and Seal of Batavia, IL. Not sure what it held, but the can was painted with a red, yellow and white label.
I know this because I found an old can with the same cap on eBay. Plus it came to me in a dream. Good enough for the benzene ring, good enough for me!
Seriously, the answer is no, I don't know what material the container was made of. None of us know and we won't know unless we find it, which will be difficult if it doesn't exist anymore. But we can ponder it a little and see where our thoughts take us.
To me, the curious question of the cap is:
How did the container vanish without the cap being severely distorted in the process?
Start with the container material. Two candidates are steel and glass. Let's take glass first.
Glass is plentiful, cheap and was in wide use for packaging at the time. It’s also brittle and dense, so it gets heavy by the time it’s thick enough to have any strength. One thing it’s got in common with lead is chemical stability, so if you want to bring some sulfuric acid on your flight around the world, a glass bottle with a lead cap would be a good candidate. I don’t like the geometry of this, though. If the OD of the cap is about 5/8 “, and the bottle neck thickness was enough to have some strength and impact resistance, there isn’t a lot of diameter left for a hole through which to pour.
Regardless of how good a container a glass bottle with this cap on it would be, we are now at the interesting question. What happened to the bottle? If it was empty and someone wanted to use the bottle as a container, the issue is removing the cap without damaging the bottle. Lead is nice and malleable; it wouldn’t take much of a tool to pry the skirt of rolled-over crimp material up and remove the cap, if you have a tool. If you don’t have a tool, you become the tool. Fingernails or teeth would probably get the cap off, but with a lot of deformation (teethprints anyone?, dental records, photogrammetry of publicity-shot smiles?). This way is, by definition, going to deform the cap and 2-6-S-45 doesn’t show evidence of this kind of mechanical trauma. You might try pulling on the spout to get the whole cap off. That might work, but it might just break the spout off. Lead also has a low melting point, so you could heat it up and hope that you don’t lose the bottle in the process. Place your bets and take your chances.
Conversely, if you wanted the cap and didn’t care about the bottle, break it and shake it. No tools needed and you’ve got a lovely little lead funnel/shot glass/ fishing weight/??? along with some glass shards.
How about a hybrid of the above? You want a nice sharp piece of glass for something. Break and shake, then throw the cap away and hope you ended up with a piece of glass that suits your purpose.
Got a gun? Shoot the glass out from under the cap! William Tell’s evil twin!
Whatever the motivation or course of events, both the lead and the glass would be durable enough to survive 70 years of atmospheric exposure, which is unavoidable. Less certain is whether an intact bottle would remain in place or be scavenged by a colonist, used as a target or float away during a high water event. I didn’t see any details about the circumstances the artifact was found under, but it seems like there was some glass located at the site. Any chance of a match?
Now to the steel possibility. Most of the contemporaneous items these caps are found on are steel, probably tinplate, cans holding a few ounces of refined liquids. Oil, white gas or lighter fluid and the type of specialty products envisioned by the caps inventor seem to be most common product. More pedestrian products wouldn’t rate such a specialized cap. I have a can of gun oil, probably from the 1940s or 50s in a steel can with a similar style but different manufacture cap. No signs of corrosion, but it hasn’t been in the same environment.
I went back and reread the first bulletin on 2-6-S-45 and the NDT work done at the Naval Academy reported a steel ring inside the “knob”, along with corrosion products on the outside that helped to obscure the markings. The presence of a steel ring didn’t seem too weird if the item was a knob for adjusting something, but to find a steel ring inside an item that was designed to be deformed during the crimping process is puzzling if not downright counterintuitive.
If you wanted to get a lead cap off of a steel can so you could use the can, you’ve got pretty much the same situation as with the glass bottle and the tools, except that a steel can could take more abuse and still function. Removing the cap without damaging it, however, is a bit of a challenge, unless you have a lot of time and some chemistry available.
So where are we now? We have a lead cap with a steel ring inside it, but no indication of the container it once sealed. A cap made of a very stable metal with corrosion products on it with no obvious driving force for the corrosion. Or do we have something a little different?
Rather than a lead cap that was cast around a steel ring or had one pressed into it, perhaps we have a lead cap with a ring of steel still inside it. The remains of a steel can? I’d be curious to see some details of the steel to see if it appears to be the rim of a spout. If the lower edges of the steel indicate failure by rust penetration, then it seems like we have a steel can that has oxidized itself into oblivion, or at least oxidized itself into separation from its cap.
Lead forms an oxide layer very quickly when exposed to air, much like aluminum. It is this layer that then protects the base metal. I am not enough of a chemist to know whether lead in contact with iron would form corrosion products without any real electrolyte other than salt spray, but perhaps someone else could comment on this.
Curiously, the leading contenders for the contents of the can would likely have opposite effects on its post-consumer lifespan. Some sort of oil or lubricant would act as a preservative, while a naptha-based lighter fluid would volatilize rapidly and leave the surface free of petroleum or other oils that might protect it.
In my mind, the most likely scenario is that a can of lighter fluid comes to the island, is used up and someone tries to take the cap off by prying/pulling on the spout, which breaks off and is lost or discarded. The can is discarded, the cap rusts off with a ring of can spout material still embedded inside and the rest of the can either rusts, floats or is carried away. The cap survives to be found 64 years later, and people all over the world relax in the evenings by pondering things that aren’t real important, but offer a chance to exercise the brain. Beats Sudoku any day.
Regardless of the container material, you end up with a couple of known knowns , and a big pile of known unknowns. Life is like that, but if you’re careful to put things in the right pile to start with, they tend to migrate to the smaller pile as you keep thinking about them. Just make sure to keep the unknowns from sneaking in to the known pile.