I am having a real problem trying to get iridescence to apply to different objects. I think most examples here (except for Lyle's) have been attempts with render clouds plasma and some filter like voronoi or mosaic. EDIT, I have also played with gradients and different overlay modes. Certainly that is where I have been trying to come up with something. It appears that the greens and blues show more promise than the deep reds or deep purples. Also a light coloured separation of colour facets seem to work better than a dark separation.
Most objects can be made to look iridescent to some degree (see the very first entry) but I think it will be very difficult to come up with a filter or a short procedure to achieve a convincing iridescent overlay.
This is a very challenging task. I shall keep trying.

Ok I have tried again with a Voronoi pattern and an emboss. I still failed to make it convincing. BTW , sorry I did not acknowledge Oregonian's effort in my last post (it looks good). I think I'll give up.

wbool63 - I think it looks very good and the pattern really works well with the colours to give the effect.

i agree with he4rty, and it looks better than my attempts, wbool

@Graechan: was that a question pointed at me ?

and what is up with your signature, that looks absolutely great !

wbool63: i agree with he4rty and esper, i think your iridescent effect looks best of all so far - especially considering you tried to apply it on an object.