White Bristle Brushes are superbly hand crafted from good quality Hog Bristle. Excellent for traditional and water mixable oils, they can be used with acrylics, caseins, and alkyds. These brushes are natural hog bristle NOT synthetic and will perform like a natural hog bristle brush. Interlocking refers to the abundance of natural flags, or splits, on the tips of the bristles.