launditch, tinning is normally done by cleaning and fluxing the inside and then whilst warm it has molten tin swilled around in it (very much like beeswaxing or pitching a leather vessel).
John fenna, I do like to try my hand at new things

Sinking is as you say hammering the metal into a hollow form, but the hollow is normally deeper than the shape you want. The hollow these were formed into is a 3" diameter slightly deeper than a hemisphere. There is a similar technique that involves hammering it into the form completely, so the hollow is a negative of your vessel; I think its called dapping but not sure? I've made a really cool brass heart for a LRP thing by carving the heart into a log and then hammering the cold brass into it with a small ballpeen and then sharpening the lines from the outside with a finer crosspeen (more repousse to finish)
Samon, they will of course be for sale. I haven't settled on a price yet though, likely to be aroud the £50 mark based on the work involved
I'm definately going to be doing more of these, I quite enjoyed making them once I got into a rythm.

I had a brief go at raising a straight sided cup today (last hour or so of the day). Didn't like that at all!

I think I just need practice, but it was realy tedious compared to sinking a nice round form. I'll keep with it until I've got it sussed and then chalk it up as an experience (likely never to be repeated).