Pick Material From Object (Eyedropper)
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(Material Editor): Compact (Pick Material From Object)

Compact Material Editor menu bar Material menu Pick from Object

(Slate Material Editor: Toolbar (Pick Material From Object).)

Pick Material From Object lets you select a material from an object in the scene. Click the eyedropper button, and then move the eyedropper cursor over the objects in the scene. When the eyedropper cursor is over an object containing a material, it fills with "ink" and a tooltip with the name of the object pops up. Click the object. The material is placed in the active sample slot.

If the material is already in the active sample slot, the eyedropper has no effect.

If the eyedropper cursor is over an editable mesh with faces selected at the sub-object level, and the mesh has a Multi/Sub-Object material applied to it, then the eyedropper picks up the sub-material. However, if the selected faces have more than one sub-material assigned to them, then the eyedropper picks up the entire Multi/Sub-Object material.