Using steam sounds interesting - I'll definitely try it on the painting I'm currently working on, since it's one I have to ship, and I've hated the effects of any fixatives I've used as a final step.
Two questions do come to mind, though:
Have you tried it to fix between layers? If so, how well did it work to 'freshen' the surface as compared to a light spray of a reworkable fixative?
Are there any particular pigments, brands of pastel or brands of paper that you've encountered that haven't 'liked' this technique? If so, which?
I've had very good luck making pastels using the pre-moistened Wallis mixes, but I've encountered a lot of problems obtaining consistent texture when mixing from 'scratch' - some very hard, some crumbly. I'll likely try mixing from scratch again ... schedule myself some time to experiment and take notes of what results I get from which mixtures.
Thanks for the info!