My Sharpie brand permanent marker seems to work better on mini blinds than pencil.
This spring I received 3 types of iris in trade from one person who was SO kind as to put a mini blind marker in the baggie with each separate rhizome. Being as I had the markers, I put them all into one large pot to wait for my eventual planting spot to be ready. When I came back in a couple of months, the pencil had faded off. Now I'll have to wait for bloom to know who's who.