Hi Francisco,
I never thought of explosives! I am sure that would be a great project. Like getting narcotics samples, the problem will be getting reference samples in a safe way. Maybe a cooperation with a testing laboratory or enforcement office?
Unfortunately I do not have such contacts.

@ Luis:
I have scanned three types of mushrooms so far (one tray purchased of each from local shop)
– King Oyster mushroom Pleurotus eryngii
– white cultivated mushrooms
– brown cultivated mushrooms a variety of agaricus bisporus
As may be expected the King oyster shows quite a difference from the common champignons
I hope to get some other varieties scanned soon.

Please remember that CP have warned that the scans from prototype devices may or may not be useful in later collections.
I am not building huge collections yet, just a few samples to see what may be promising, and to test the software.