When the checkering is all done, if you dip a toothbrush into the tru-oil, or whatever your finish is, try rubbing the brush on a black lumber marking crayon. The oil will dissolve a bit of the wax crayon, and the lines will look like an old classic checkering on a stock, that has some patina(hand grime, really). You can go over the pattern, putting more crayon black to even out the shade of darkness, or wash out the brush with thinner, and lighten out the shade, if it's too dark. Ilove the look of an old oil finish stock, but I use Formby's Tung oil, with woodworkers warehouse aniline powder red-brown oil soluble dye stain added to get the old alkanet root/linseed mix color.