That was my first (and only, so far) time doing something like that -- no plans or guidelines -- I was flying blind also. Even after some serious sanding of the old blade tip, the tip edge was a bit raggedy, and what I wanted to do was to cover and hide the tip edge as much as I wanted to protect it.
So -- I just added graphite to the epoxy until it felt right to me -- thick, but still liquid, like thick pancake batter, perhaps, so that epoxy coating went on perhaps 1/16 " thick. I cut the masking tape with an exacto-type razor knife, and then put much extra tape below the working area in the event there were drips. I made the black strip as narrow as I did so that the masked edge would be just where the edge of flat of the blade turns -- the little ridge that masking inevitably leaves was less apparent that way, and more readily minimized with a bit of sanding. I also considered making the epoxy band abut 1/2" wide around both sides of the tip -- but felt I might have more problems with the epoxy not coating evenly and showing runs, etc., and I was concerned with adhesion over the stain -- not a problem on the end-grain edge. The risk with the narrow band is that, being narrow, it would chip more easily. I imagine that you could make the epoxy coating a bit thicker by creating a dam with masking tape, as Todd mentions, but I'm not sure how durable it would be without something other than graphite as an additive, again as Todd mentions.
But as I say, other than thinking that it looked pretty good when I finished it, I have no information about how it actually worked out in use,
Unusually for me, I don't have any other pictures, not even of the finished job. With a digital camera, I usually give into the temptation to take too many pics, but for some reason, I didn't this time.