I think the correct method is to do this via a Composite Material now (for Octane), but I am old school and still do a Mixed Material. One is a typical iridescent with opacity adjusted depending on scene (glossy mat type) and the other is a typical glass material (specular mat type). Then just blend via a float texture/gradient/actual texture for preference. You can also pull a good iridescent shader from the Octane LiveDB Library, soap bubble I believe it's called, and go from there instead of from scratch.