The crankshaft is glass. The piston is glass. The counterweight that makes the wheel spin evenly is glass. Imagine that everything is made out of glass. * There are no sealants used. All is accomplished by a perfectly snug fit.
image/text credit: steam glass
The gap between the piston and its compartment is so small, that the water that condensates from the steam seals it shut! * Notice the elaborate excessive steam exhaust system next to the piston.
The piston is the most arduous part to make due to to extreme level of precision needed. Its parts have to be so accurate that no machinery is of use here.
The piston and its cylinder must be hand sanded to perfection, and they are very likely to crack in the process! On average, three out of four crack.This Model of Stephenson’s Steam Engine was made in 2008 by master glassblower Michal Zahradník.