Practice question · True or false
Chalk reads as an opaque white in a water-based medium and almost disappears in oil, because linseed oil's refractive index is close to chalk's and air's is not.
Hints
- Compare 1.48 and 1.57 with 1.00.
- Scattering depends on the difference, not on the pigment alone.
Show the answer
True
Why
True, and it is the most useful single fact in the lesson. Chalk against air differs by more than half; against linseed oil by under a tenth. The particle is identical in both cases, so opacity is never a property of a pigment on its own but of a pigment and the medium around it.
Practise Aqueous Media
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