Problems with Argentium age hardening

I have repeatedly tried to age harden argentium by holding at 550F
for 1+ hours; however, the metal always seems more annealed than it
was before I started. I have tried the process in my trinket kiln
and the kitchen oven.

I am wondering if the air cooling rate is critical. I have been
using small pieces and at the end of the holding at 550, I remove
from the oven and the pieces cool very quickly (less than 30 sec). I
tried leaving in the oven to cool more slowly then removed when the
oven was down to 250F. At first, the piece seemed like it might be
hard, but when I went to bend it, it was very soft.

Before I continue my fruitless trial and error, I thought I would ask
for any suggestions on what I am doing wrong.

Thanks. Rebecca