Most tack makers have a similar progression: we begin with whatever we can scavenge and make, moving on to better materials as our skills outgrow cobbled together supplies. One of the natural parts of this progression is realizing that you cannot rely on found leather. There comes a point when you decide that you need to take the jump and buy natural leather. Unless you intend to only make light oil western pleasure saddles forever, you'll need some dye to go along with it.
For our purposes, there are three ways of coloring leather: water-based dyes, oil-based dyes, and leather paint. My experience is predominately with water-based dyes and paints, so that is what will be covered here.
I use Tandy's Eco-Flo line of dyes. Sad to say, there isn't a particularly well-thought out reason. When I decided that I needed to make the jump from hobby store scrap bags to dyed leather, I was still in high school. My mother was supportive, but worried about the new carpet and so the water-based dyes were the only sanctioned ones (there was, by the way, only one spill in the entire four or six years I dyed leather at my parents!). Even though I'm long moved out, I haven't tried oil-based dyes. I like the simplicity of the water based ones - they're easy to mix, easy to water down, and clean up nicely. I'm sure there are great benefits to the oil-based dyes, too, I just haven't had the chance to experience them.
To dye leather, you'll need:
A protected surface to dye on (you can cover your surface with plastic sheeting, tin foil, wax paper, or work in an old tub, tin pie plate, etc)
Brushes, wool daubers, or cotton balls
A scrap of fabric for buffing
Leather (uncoated vegetable tanned)
Here, I've gloved up and laid down tin foil to protect my work surface. Water-based dyes can be cleaned up with soap and water, to an extent, but any porous surface or material isn't likely to survive dyeing.
I'm covering a large area of leather, so I've chosen to use a cotton ball as an applicator. Wool daubers are also a great option - they have a long stem to help control mess. I'm a bit of a cheapskate and would rather not buy them when this works fairly well. The bottle of dye I'm working with is almost full, but when it's lower I'll grip the cotton ball with my pliers and wrap the handle together with a rubber band to keep them shut. It works quite well, but I make sure to thoroughly clean the pliers when I'm done.
I've dunked my cotton ball and I'm ready to apply! I apply dye to dry leather. You can work in lines, from side to side...
...or in circles. If you're using a brush, I recommend mixing it up to help reduce streakiness. Keep going until the top of the leather is saturated.
You'll know you've done about all you can do when the dye no longer soaks into the leather immediately and instead pools a little - you can see a bit of that in the lower left corner of the piece above. When that's done, flip it over.
Dye the flesh side, too. I find this gives the most consistent color. Once you've saturated the back, the piece will be quite damp. Set it aside somewhere safe to dry. I usually move mine to the top of the printer that sits just beyond my desk.
This is why you use gloves! I don't have a photo of this step, but once my leather is completely dry I use a scrap of fabric to buff the smooth side. This helps remove any residual dye and gives the leather a nice, healthy glow.
Different kinds of leather will take dyes differently. If you dyed tooling calf, skiver, and natural lace with the same color from the same bottle, you would probably notice some color discrepancies between the three. I'm afraid this is normal - if you really, really need everything the exact same color, it's best to use the same hide and cut or thin leather as necessary for your needs.
Streaks can happen. Shaking your dye bottle well before beginning, using a sponge/cotton ball/dauber rather than a brush, and moving in circular motions will likely help improve streaks. If you still see them, a second coat on the smooth side will help even things out. Some streaks may be the result of your leather - check the hide for odd wrinkles or imperfections if you notice anything really strange in the way your dye takes.
If your leather has an odd greenish-metallic cast, your dye might be going bad. I've had this occur on dyes that had been opened for 6-8 years; you might see if you can figure out how long you've had them and consider replacing. Shaking really, really well and buffing the leather after it's dry can help.
Always, always, always seal dyed leather. This not only protects the leather, but protects the model. Even once sealed, dyed leather has the potential to stain. In my experience, particularly dark colors or vibrant colors are most likely to do this. I always recommend removing tack from a horse as soon as possible, just in case.
Dyes can be diluted with water or mixed to create custom colors, but I'd avoid mixing water-based and oil-based dyes together.
I typically trace, tool, dye, then cut out pieces for a western saddle, while english saddles are usually cut from a larger piece that I've already dyed. I find that dyeing after tooling helps define the carving I've done, though occasionally I need to go back and refine some of my lines. Some people prefer to dye first, then tool - if you aren't sure, try it both ways and see what works for you.
This may be an issue only with Eco-Flo dyes, but even when it's soaked on both sides you may find that the flesh (or rough) side of your leather isn't the same color as the smooth side once you've skived it down. I don't usually worry about this, except with reins. I typically go back over the back side of the reins to even the color out.
Be very careful if you plan to dye more than one color in a given day. If you're going lighter, make sure that your work surface and tools are clean so that you don't accidentally contaminate your lighter dye.