I remember 'way back' when I was 'into' dying lots of tying material. What a time it was; what a mess I usually made of things. I think I can safely say that at least 90% of what I dyed failed. I remember a tendency to over 'cook' hackle necks. 'Rendering' is the operative word here. Dark, blue/black pieces of chicken hide with a few pathetic feathers still clinging to them. My version of blue-dun.
The sulphuric acid treatment on the rabbit hair (makes it yellow) actually did work and I tied with that chunk for years. The deer hide (whole) in the vat for months (alum as I recall) never did get soft. I was supposed to beat it over a stump I think. I remember 'cooking' a pair of leather gloves once too, but for the life of me, I have no idea why I did that. They shrunk and turned into 'cracklins', kinda. Fun times. Mostly didn't learn anything of any value. But did have a grand time. You might give some of it a go.