Wow, this is a really cool and informative thread. Is there any chance that the brief time in boiling water could mess up the heat treatment of the metal? Do you think the dye would also tint the enamel on the interior of one of Case's colorful shields?
I'm getting ideas here...
As Blue Sky rightly pointed out, the boiling will not have any effect whatsoever on the heat treat.
The point about epoxy is a good one though, the usual way to remove epoxy is by boiling in water!
I have tried to pry out the shields on the knives, and they don't seem to have been affected, even one that I superglued in after it fell out a while ago.
I guess they don't use epoxy to attach the shields, but it is a very valid point and something to watch out for.
As to the enamel, if it is actually enamel, it is basically glass, so I can't see how it would be affected as long as the knife wasn't heated/cooled too fast.
I'd drop the knife in another pot with plain water, gradually bring it to a simmer, and then transfer it into the simmering dye. Once the dyeing had finished, I'd transfer it back into the simmering plain water and let it cool down naturally.
This would probably be best practice for all knives anyway, because it would decrease the chance of bone cracking through thermal shock.
There's always going to be an element of risk, but I don't think it's a big one.
If the enamel is fake, all bets are off.
The easiest way to tell is to hold the enamel against your tooth and move it slightly. If it is real enamel, it will feel hard, if it is plastic, resin etc, it will feel soft.
In other news, penetration may be better than I thought.
My RR barlow broke!
I took it out of my pocket, and the backspring on the small blade went 'ping' and part of it flew off

Nothing to do with the dyeing process of course. I don't blame rough rider either, these things happen, and from a google search for 'broken backspring', seems to happen most often on Queen knives. Couldn't find any references to a rough rider backspring breaking, so I guess it's an isolated incident.
Anyway, I have dismantled the knife, hoping to reassemble it without the small blade, to make it into a single blade barlow. It's been interesting so far, and I'm enjoying learning about how these things are put together.
In the process of dismantling the knife, I removed the scales.
The scales were held on by some kind of rubber cement, presumably just to hold them together during assembly until they were pinned.
I noticed two important things:
The inside surfaces of the scales were black.
The inside surfaces
under the adhesive were black.
The first could be explained away by dye seeping under the scales while the knife was submerged, but the second one not so much.
The adhesive was still very thoroughly stuck to the scale, and I had to use a razor blade to scrape it off. The adhesive itself was not dyed black, it was red in color.
This seems to me like the dye must have penetrated very deep, through the thickness of the scale in fact.
When I sanded the canoe as explained above, I got through to red, but it is very dark red, not like it was before I dyed it black.
I think they dye penetrates pretty deeply, but is only absolutely jet black for a certain thickness.
Hopefully, this is very good news. It tells us (I think) that they dye is getting very deep into the bone, but needs to be simmered for longer to get good color saturation.