What are iron nitrate and tannic acid, and why do people use them?
Iron nitrate, also called aqua fortis or ferric nitrate, is the traditional stain for a maple stock. You brush it on, then activate it with heat, and the color blushes from a dull grey-green to a rich red-brown. On curly maple, brushing on tannic acid first deepens the contrast in the curl, giving the striking black-grey figure builders prize. Neutralize any stain that reaches the barrel channel or inlets with a little baking soda and water so nothing rusts underneath later.