Mushroom: old Phaeolus schweinitzii (Norwegian: gulrandkjuke, English: "butt rot" - tee hee)
Here is what old gulrandkjuke looks like before it's dried.
Mordant: alum (details about the mordanting here)
Ratio: 1:5 (5 g of dried mushroom to 25 g merino yarn)
Result:

And then! I found a whole bunch of Cortinarius Friday afternoon!!

Mushroom: Cortinarius semisanguineus (Norwegian: r?dskivekanelsl?rsopp, English: Surprise Webcap or Red-gilled Webcap)
Mordant: alum
Ratio: 2:1 (20 g of dried mushroom to 10 g merino yarn)
Result:

*sigh* Isn't it gorgeous??

And this...

... (inspired by Adrian's adorable mushroom pulse warmers) is what I'm making with the yarns!