Not only is the question of the secret object no longer important, the problem is instantly solved. On a small piece of expensive, acid-free, cotton paper, guaranteed to last centuries, two words, my name and my accomplishment: Keller fecit.
After dating the paper, I rolled it so that it fit into a small metal capsule. I loosened the replica’s screws and placed the capsule gently inside the ball of twine. After tightening the screws I gave the replica a slight shake and exalted in the hidden noise.