Forge version: 10.13.2.1236
Mod version: 1.2 (I attempted to use the versions from the auto build, they seem to error on load)
Other mods: http://tinyurl.com/wwpack

Everything I can find online seems to state that you should be able to convert shells back to golden nuggets as a shapeless crafting recipe. This doesn't seem to be the case at the moment.

Old known issue, was resolved in newer dev versions. If you're getting crashes in newer dev versions, you likely need to delete your lib sandstone. I'm not making fixes to branched versions of Reliquary, the new ones are operable. Let me know after updating to a dev build and the newest libsandstone that your issue is still present. If you're getting crashes with the newer dev builds after following the upgrade directions, you should be posting those issues here. This one, however, has been resolved for a while.

Also note that in the newer versions it is four shells to a nugget, instead of a 1:1 ratio. If you don't see the recipe in NEI, it flat-out isn't working. But I can confirm that the older dev versions had this issue and it has been fixed, within the last month and a half or so.