Baltic. If you take a peek at
this thread, Mike posts some info on cold dyeing.
In reality, if you buy a pot of Veniards dye it gives you very basic instructions in the packet. When I first started dyeing I followed those and got reasonable results.
Step 1) Soak and degrease your feathers.
Step 2) Bring water to the boil in a pan.
Step 3) Add as much dye as will fit on the end of a pen knife (I used a tea spoon).
Step 4) Let water cool to simmer, add cold water if necessary. Add your vinegar.
Step 5) Put your feathers in the basket and add to dye bath.
Step 6) Watch your feathers until you get the right shade.
Step 7) Wash feathers in cold water and dry them.
This is very simple and will give good results. It's pretty much stick it in a pan, don't let it boil and watch for your shade.
The step by step I've provided is a bit more convoluted but gives
consistent results. I found that reproducing a shade is a fair bit harder than producing it in the first place, hence good note keeping of all the variables.
Cold dyeing will still require that you degrease your feathers, measure your dye and watch for your shade for good results.