Who said it was "hard" to iridise? The method and processes are well known.
tricky to do, is to iridise previously manufactured items using heat. That's what I was saying is......
"the technique (that) took great skill and experience"
For example, Terry Crider used cold "blanks", re-heated the items to 1000 f, then iridised, and heated again in a glory hole. He told me that when he first began iridising blanks, everything took two applications and two separate firings. In fact some pieces took three applications and three firings. As Terry told me "there were a lot of breakages this way"!
That's what I was referring to in my posting above.
The LGW method was vacuum iridising. I am not aware of anyone else using the method - and the result is a very vibrant and easily recognised iridescence.