On Tue, 01 Nov 2005 14:35:30 +0000, Timothy Murphy
wrote:

I assume the chair itself is made of oak,

If it's Irish, it's not safe to assume anything. Shortage of timber led
to any old bit of tree finding its way into furniture.

It's also somewhat unlikely to be made of oak in any part. Generally the
favoured timbers were elm for the seat (it doesn't split in narrow
cross-grain sections) and either beech or ash for the spindles and
hoops, because they steam bend and turn nicely. They also coppice well,
particularly ash, as a source of fast-growing cheap spindles.

Oak doesn't bend or turn well and it grows in big pieces on slow-growing
trees. If you have oak, use it for big flat boards instead of turnery,

but what would this bent strut be made of?

Be careful working on truly old Windsors. They're surprisingly valuable
- especially Irish chairs.

Try putting some photos onto the web, then asking in rec.antiques.
There's a knowledgeable chap in there from Northern Ireland who might be
helpful.