Has it really been over two years since we bought our tetsubin? Time flies! I think that we bought it from Artistic Nippon, and it has served us very well. I think it's a perfect pu'er pot. It brings out the mineral-like characteristics of the tea, and swells it nicely.
(Silver kettles are not really my thing - and we don't drink a huge amount of wulong.)
Here's our little baby when it was newly arrived, as described in "Nembu Tekki":
The original kettle
As yet unaffected by use! Note the particularly clean spout, shown above. After one year, I took the following photograph (from "The Aging Tetsubin"), in which you can see some chalk accumulating:
The spout after one year
Now our pot is coming on for being two-and-a-half years of age, and it has quite a build-up:
The spout after two years
However, most interesting is what's been happening on the inside. Shown below is the original pot - note the orange spots of rust that came with it (and which are entirely normal for tetsubin), and the central mark which is a result of the fabrication process:
The original interior
After one year, it looked as shown below, where the rust-spot has grown to cover most of the fabrication blob, and where some chalky sediment has been accumulating:
The interior after one year
Now, after two years of heavy use, the base is almost entirely coated:
The interior after two years
...which we can see a little more clearly if we zoom in:
Detail of the interior, after two years
I am very careful not to disturb the interior of the kettle - we pour water in, pour water out, and dry it by leaving it on the warm hob for a moment after each session. So, the above has accumulated simply through use - between sessions, it sits entirely dry.
We use spring water for almost all of our sessions - had we used the tap water here, it would no doubt be several orders of magnitude more white. Even with "good water", the process is obvious.
So, don't fear a little chalk or the odd spot of rust. I remember seeing some old kettles in which the sediment had formed a thick mat inside the kettle. I rather like it; it is like the patina on a teapot - a sign of use.