Hierarchy classification:

1. top of the aat hierarchies
2. Materials Facet
3. Materials (hierarchy name)
4. materials (substances)
5. [materials by function]
6. colorant (material)
7. pigments
8. [pigment by color]
9. blue pigment
10. synthetic organic blue pigment
11. Prussian blue (pigment)

Anotations

Scope note:

An oily film of Prussian blue pigment formerly used in machine making; it was placed on machine fittings, then the parts were rubbed together; the removal of the pigment indicated the position of high spots or rubbing between the two surfaces.