Not sure if this kind of product placement is allowed, but I use Bristows extra firm hold hairspray (and no, they don't pay me for saying it). Perhaps UKGE could start stocking it...?
It works exceptionally well on pyrite, but is also very good on phosphatic bones and chitino-phosphatic remains such as crabs, lobsters, insects, ect. I also use it on certain types of bivalves and brachiopods, but that's more for the sake of apparance than preservation. Shark's teeth, especially worn and scratched ones from the London Clay, also look much better. It brings out the shine of the enamel, reduces visible scratches, and doesn't spoil the look of the root.
It also brings out the finer surface details on, say, crabs from Folkestone, and what's more, if they are a little beach-tumbled, it reduces the appearance of external scratches considerably.
Ensure that your specimens are completely dry, place on a towel or non-fluffy piece of fabric outdoors, in the sun, and then spray very thinly and quickly over the surface from about 50cm+ distance. Always use outside, where ventilation is not a problem, and wear a protective mask just to be on the safe side.
Let each coat dry for a minimum of 2 minutes, and when spraying, ensure that you DON'T do it slowly and linger over the fossil - short sharp bursts is what you want, to ensure a fine coating - otherwise you will end up with a coating that is too thick, and in this case often turns white and opaque. If this happens, wash the specimen thoroughly in warm soapy water, let it dry, and then try again.
The spray itself is perfumed, and I don't much like that aspect of it, BUT, give it a week or two and the scent dissipates entirely from the specimen.
CAUTION: If you use this method and then wash your fossil you will lose some or all of the protection. You can 'dry' clean them, but just bear this in mind if you get them wet, as in the case of pyretic fossils, you might wish to dry them out and spray again afterwards.
I would wholeheartedly recommend this alternative to any PVA addicts out there, as if you don't like it, you can just wash it off and apply PVA afterwards...
NOTE: Every single ammonite you guys have seen in my posts are preserved in this way, even the nacreous ones from the Gault..
"We try not to use the word insane, we prefer the term mentally hilarious..."