Early air tanks assembled with solder??

[Swingpress]

So as some of you know, I acquired an old compressor and tank awhile back and while the pump was salvaged the tank was ****. Well today I started to turn it into a quench tank for large pieces. I used the torch for initial paint removal on one end because I make good choices. And the are where sidewall meets end cap moved! What a surprise I found!

Anyone ever seen anything like this?

 

[Corndoggeh]

What is the tank material?

 

[Craptain]

That looks like copper. I would not have expected that. I think it may have been a converted water tank.

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[Swingpress]

It's a steel tank. Looks like the end cap rests on the inner edge of the main body.