What's the best material for an ignition tube?

Over the last couple of years I have read everything I can find about the materials used to make the tubes for Hot Tube Ignition in gas engines. The general view around the early 1900s seems to have been that iron was cheap and worked well, but was not very durable, tending to close up internally after a while. Porcelain was more reliable in the long term, but was very fragile and easy to break. Nickel was counted better than iron but I can find very little detail about its use.

Porcelain can be discounted for present day use, except for engines that were designed for it (if spares can be found). To iron - presumably wrought iron at that time - and nickel, could now be added stainless steel, which I have seen used in the form of a bored out bolt.

My questions are these:

* Was pure nickel used, or was it an alloy and if so which?
* Has anybody any knowledge or experience of using nickel tubes?
* Has stainless steel any drawbacks?

Any other information or reflections would be welcome.

George

I would think iron was used because it is good at retaining heat.
Chiefy.