This is the best I could come up with. I suspect you would need to research how damaging or healing coal tar might be.
V-tar is a crude coal tar product that has been formulated to be water soluble, so it won't stain skin. It is applied once a week, left on for 5-6 hours (or overnight), then removed. Users must avoid sun exposure for 72 hours after treatment. Sun exposure is not required for treatment with V-tar, making it attractive to those who prefer to minimize the contrast between normal skin and vitiligo, as well as those who are unable to use light therapy due to other conditions. V-tar can be used by anyone, including children.
Vitiligo Support International - Vitiligo Topical Therapies
V Tar Liquid RX (30% whole coal tar) made by Dermasave Labs in Pleasant Valley, NY.
Apparently, it takes at least 3 months to see any results. It does not help everyone. This is all I gleaned from other health forums.