I learned about the technique from
this post by Flying Guillotine. And followed the procedure described
here by jamesbeat.
The formula for this one was a moving target. I did some research on the RIT dye webpage and found a mix that was close to what I wanted (Chile Red, #143). I already had two RIT liquid dyes similar to ones in the recipe from the work I did on my mini copperhead, so I substituted sunshine orange and dark brown for the recipe's tangerine and cocoa brown, and purchased a bottle of scarlet.
Saturday evening I experimented with mix proportions, and found one I thought would work. It was:
1/4 teaspoon dark brown
1 teaspoon sunshine orange
3 teaspoons scarlet
When it came time to do the work Sunday afternoon I used the same proportions, but mixed enough to add to the approximately 2 cups of water in the pan. The mix in the pan was:
1 teaspoon dark brown
4 teaspoons sunshine orange
12 teaspoons scarlet
I checked it periodically, by removing the knife from the dye solution, and dipping it into water I had heated to similar temperature. At about 10 minutes in I didn't think it was dark enough, so I added another 1/4 teaspoon of the dark brown.
It was still too orange, so twice (about 10 and 15 minutes later) I added another 3 teaspoons of the scarlet.
After about 35 minutes in the dye I turned off the heat and began the cooling process.
I think I may have left it in a bit too long, or used a too saturated dye mixture, because I am experiencing some dye rub off onto my fingers, which did not happen with my mini copperhead. Or maybe I did not let it simmer long enough in the dye solution after adding the final scarlet addition?
Hope that is helpful.