Magic-dampening Spikes

In A Murder of Mages, the killer had magic-dampening spikes that immobilized his mage victims. They seemed to have an anesthetic effect on mages, but not those without magic. Victims would not feel the spikes that held them down.

Eight were retrieved from various crime scenes. One was left with Major Altom Dresser to investigate, while the others were stored at the Inemar Stationhouse. They did need to be hammered in, but did not show the denting that iron would have. They came out of the victims surprisingly easily.

These were not constructed like mage-shackles, which are steel mixed with dalmatium. This leaves them as something unique in Maradaine.

These "Eight Fallen Pins" were stolen from the Brotherhood of the Nine.

Minox Welling sensed that something was amiss with them, and in An Import of Intrigue, the seven spikes and all records of their existence, had vanished from the Constabulary station house.

Loose Ends
What are the spikes made of? How do they dampen magic? (Do they perhaps repel rather than absorb numina?) Are they artifacts of Physical Focus, Will, Faith?

What did the Brotherhood of the Nine want with them? Were they for the Winged Convergence spell, or after?

Where did they come from? How did they get to Maradaine? Who in the Brotherhood handled them? How did the Murderer of Mages gain possession of them? Who removed them from the Inemar Stationhouse, and how were the records altered? Where are they now (e.g. mid-1215)?

What are the long-term effects on mages who've been spiked?