Sheila Joyce, the hook used in that pattern is comparable to a size 14, which is very, very small. When I use anything smaller than a 10 I usually end up wearing a temporary hole in one of the fingers on my left hand where the hook end rubs across it. The DMC 100 thread is comparable to sewing thread. I have worked with size 30 and it is too fine for me. I can't imagine working with thread that fine.
Well, since I have no use for that collar right now, I will pass on it. But I do think it is the prettiest one. The smallest hook I have is a 10, I think. I hae never seen a 14! And I do crochet the very fine thread too loosely to get that look, I fear. But it would be fun to try.
I have never done Irish crochet, usually do not like the look. But this one is lovely. Guess since my maiden name is Murphy that I ought to give it a try some day!!!