Scientific American 41, 3.7.1847
Put two ounces of indigo into four ounces of oil of vitriol, (sulphuric acid) about two weeks before you want to color, shaking it well every day. When ready for coloring make a strong decoction of black oak bark, sufficient to wet what you design to color. To this add one pound of alum to every eight pounds of yarn, stirring it till all the alum is dissolved. Then pour in of the mixture of indigo, till you think you have it of the shade desired. - Then put in the yarn, as much at once as you can; let be over the fire for twenty-five or thirty minutes; then lift it out to air for a few minutes, and then return it to the kettle and let it simmer three hours, stirring it frequently. The two ounces of indigo will color about ten pounds of yarn deep green, and five pounds pale green. The pale green is managed in the same way, only use a less quantity of indigo.
The above receipt is taken from the Ohio Cultivator, and it is different from the too many published, because it is a correct one. - Fustic, however, till answer in the place of oak bark. The indigo must be powdered and of the best quality.