[pcm81]

I am making a small experiment with dyes and am curious about your opinions.

Very basic theory of operation: fiber reactive dyes dissolve in water, with addition of epsom salt the dye falls out of water and onto natural fibers like cellulose. Addition of soda ash raises the pH which causes the coloring dye to bond to cellulose via covalent bonds.
https://www.dharmatrading.com/techniques/batik/fiber-reactive-dye-chemistry.html?lnav=techniques_batik.html

Fiber reactive dye can also be used as an acid dye at low pH values to color things like nylon, but in that case ionic bond is formed, which is weaker than covalent bond with natural fibers.

I am interested in coloring some leather (real leather not synthetic crap) so i ran the experiment of using a fiber reactive dye in high pH solution. Basically i used it like i would if it was used for natural fibers like cotton. The leather came out black, so it matches the dye color I used. My question is about the chemical bonds in protein material like leather vs vegetable material like cotton. Did i create covalent bonds in leather hence i can expect the same longevity as i would in natural fibers or did i create something else that colored the leather but will soon fade? Quick wash in water and soap seem to not remove the color.

EDIT:
I did some googling about leather dyeing before embarking on this experiment and what i bound is allot of references to oil and alcohol dyes, but they all seem to be just surface treatment. This method colors the leather throughout.