Early in 1786, Raspe produced a brief but well-executed conspectus of the arrangement and classification of the collection, and this was followed in 1791 by "A Descriptive Catalogue," in which over fifteen thousand casts of ancient and modern engraved gems, cameos, and intaglios from the most renowned cabinets in Europe were enumerated and described in French and English.
The two quarto volumes are a monument of patient and highly skilled industry, and they still fetch high prices.

The elaborate introduction prefixed to the work was dated from Edinburgh, April 16, 1790.
This laborious task completed, Raspe lost no time in applying himself with renewed energy to mineralogical work.

It was announced in the _Scots Magazine_ for October 1791 that he had discovered in the extreme north of Scotland, where he had been invited to search for minerals, copper, lead, iron, manganese, and other valuable products of a similar character.

From Sutherland he brought specimens of the finest clay, and reported a fine vein of heavy spar and "every symptom of coal." But in Caithness lay the loadstone which had brought Raspe to Scotland.

This was no other than Sir John Sinclair of Ulbster, a benevolent gentleman of an ingenious and inquiring disposition, who was anxious to exploit the supposed mineral wealth of his barren Scottish possessions.