Cheers Michael. Thanks for sharing. I also have a habit of handling my iron tsuba daily.
My routine, I will select one tsuba from my collection and carry it with me to work or wherever I go for (usually) at least a few days. Rubbing it while driving, while at work, while watching tv, etc.
Many many years ago, a sword polisher I became aquatinted with while living in Japan suggested that the natural oils help stabalize the patina of iron tsuba, and I honestly love the tactile feel. It feels like therapy sometimes.
If I have a piece with some active rust, I usually apply a small amount of choji oil with a q-tip, then rub it in a bit and use a cotton cloth to rub the area. I've never used bone or ivory, but occasionally a fingernail.
I try to cycle through my pieces to give each one attention fairly, but I have to admit I have my favorites.
Damon