the reason violets are the longest lasting stain is because there are 3 primary colors: red, yellow, and blue. as far as the molecules that make up these three colors, the blue molecules are the largest, red being the second largest, and yellow the smallest. being that the red and blue molecules are larger, once they are lodged into a pourous surface they are more resist to removal where as the yellow molecules are smaller and can be removed from pourous surfaces with greater ease. thats why if you ghost with iodine the result is more redish brown because the underlining pigmentation of iodine is yellowish-redish and the reds fill better than the yellows. orange minus yellow equals red.
speaking of iodine, i found some for real cheap. never personally used it in my inks before though. anyone here have a good color recipe designed for use with iodine instead of gv? please share with rinse.