Hi, I've recently found some lovely pyrite ammonites from Lyme Regis, and I was wondering if anyone had any tips for preventing pyrite decay? So far I've soaked them in water to try and remove the salt and i'm going to try and keep them in a low humidity environment. I was wondering if there is anything else I can do such as varnishing them?
With reagrds to soaking them in water to de-salinate, it's important to use a large volume of water and change it often. One of the best ways to do this is put your little fossils inside a pair of tights, and then stick that inside your toilet cystern for a few days: every time the toilet is flushed, you get new fresh water to rinse away the salt content.
As for preservation, let them dry out for at least a week first. After that, you might want to try soaking them in a 10% solution of PVA (in water). Alternatively - and this is the method I use - buy a tin of extra firm hold hairspray, arrange them on a towel or similar, and then gently mist them about 3-5 times on each side (hold the can about 30+ cm away, and spray in short sharp bursts). This has the advantage over PVA solution in that, if you over-apply it, and end up with too thick a coat, you can clean it off in warm water (with a toothbrush), let the fossil dry out, and then try again, until you perfect the technique.
They will initially smell of hairspray, but that soon goes, and it gives a lovely finish.
*NOTE*: some beach-found pyrite ammos, if already quite weathered and salinated, will disintegrate almost regardless of what you do to them. Some you win, some you (invariably) lose.