The more I look at that thing the more I think that cylinder looks exactly like a cut-down hypodermic syringe. Commercial glass syringes have that same finely ground appearance on the inside (and on the piston that fits it) and a similar rolled edge at the top.

I certainly don't want to demean the fine work of this craftsman but, if I were to set out to build a glass steam engine, I know I would first start looking for a syringe. For obvious reasons, syringe pistons fit tightly so, to relieve the piston-cylinder friction, a bit of honing would have to be done on the piston. I still have no idea how he managed to get the gudgeon inside the piston and attach the connecting rod.

Just in case you're wondering why glass syringes still exist...

My once-obstetric-nurse daughter tells me that the doctors like to use them when administering an epidural during delivery. They say that they get a better "feel" for where they are in the spinal column with the feedback from a glass syringe.

My guess for why this may be true goes like this...

Plastic syringe pistons have a rubber-like tip which acts as a seal. This might lead to a tiny bit of stiction that wouldn't faithfully transmit the back pressure from the spinal fluid. Glass syringes have no such seal and could thus be more responsive.