Never tried jeans, so don't really know. Plus, it depends on a lot of variables (strength of dye, temp, original dye color and fading). But here's how we generally do it at reenactments: Smash a bunch of walnuts into a large pot of water. No set amount, but lets say, about 1/3 of the pot volume is walnuts (hull, nut and all just cause it's easier). Boil it up for 1-2 hrs. If it's a small pot, you can drain the water/dye into another container so the leftover debris wont leave uneven spots. Otherwise, periodic stirring will keep things fairly even. Keeping it warm, but not hot, about a half-day soak will give you about the full color of the garment. Soaking all day might give you a couple shades darker, but it probably wont be much more. Soak, then rinse in really cold water to help set the dye, rinse until water is relatively clear. The material your pot is made from will effect the color some, but I've only used cast iron for clothes which gives a nice chestnut brown to white garments. I've used a blue ceramic pot when dyeing traps, and it seems to give it more black/grey qualities?