Raise the water temperature slowly. For 3-4 quarts of water to come to a simmer, it should take approximately 30 minutes. The longer you leave the yarn in the dyebath, the deeper the color will be, just like dyeing eggs. Different dye materials, however, will dye the yarn at different rates. For paler colors, check the yarn 15 minutes after the dyebath has come to a simmer.
Most dyes require a half hour of simmering for a nice color.
If you leave the yarn to cool in the dyebath overnight, you might get an even deeper color. Just a little iron in your water can cause your colors to become duller. If you want perfect results, use distilled water for your dyebath. If you decide to take your yarn out of the dyebath before the water has cooled significantly, let the yarn cool before you rinse it. Do not put room temperature yarn into a hot bath, or hot yarn under tap water .