Chris, Tom, et al,
Regarding the crystals: I have been using Shapeways N scale FUD and FXD prints for just over 5 years now. Mainly only on the inside of some prints I have encountered this problem. I believe this issue is related to the cleaning process. If the remnants of the support material are not completely removed, they will ooze out over time, destroying your paint job (the shells are porous.....). First I used Goo-gone (which is hard to get and expensive in The Netherlands) but was not satisfied with the result: shells remained too sticky in my opinion. So I reverted to "wasbenzine", which is nafta based and (I believe) similar to Bestine. Its also called lighter fluid overhere and used by drycleaning shops. Highly flammable and not good for your health. I use it only inside my spraybooth which has a good fan with and outside air outlet. I soak the prints for 24 hours and let them dry for another 24 hours inside the booth (fan running and NO fumes in my trainroom). Afterwards the prints are completely white with remnants of the support material still sticking to the shells especially below overhanging detail.
First I tried to remove as much as possible of this dusty white stuff with an old tootbrush or scalpels (not damaging the details) but reverted to the AIR ERASER treatment a couple of month ago. Now I simply blast all the white stuff away........ leaving a very clean and also smooth shell.
Regarding the AIR ERASER, its use and safety measures: see my post "using AIR ERASER in 3D print cleaning.... TERRIFIC" in The Railwire chapter "3D PRINTING". Also the answers and additional pictures. The results of this rather cheap treatment greatly improve the quality of the Shapeways prints. As stated in the post: use the eraser inside a closed transparant box: the grid flies everywhere otherwise.........now you can re-use it and the closed box also keeps moisture out). Damage to detail is barely visible or non-existent and the shells come out very clean and a lot smoother (detail is much crisper). Also a lot of lightly visible stairstepping is gone. Additionally use a good leveling primer before painting (highly recommended).
If questions remain please let me know. Good luck, Dirk