Back to the subject of NATURAL non wood turning materials, many antelope have horns solid enough to get good pen blanks from. The best I have found is gemsbok, but I have done blackbuck and Impala. Both domestic and exotic oxen and cattle horns may be solid enough at the tips to use. American Bison horn usually yield one half blank per side. African cape buffalo look to be quite solid and might yield quite a few high quality blanks. Asian water buffalo horns, although large, are quite hollow and only the largest have solid tips large enough to use. True horns are composed of hair fibers held together in a matrix of keratin, and can tend to split between these fibers. I have found that using black ink to color the splits, then filling with CA can give an almost imperceptible repair. Of course Ivory is quite suitable for pens, both the fossilized Mammoth and mastodon versions and modern ivory, either preban from elephants and whale species, or new harvested from nonprotected animals like hippo or warthog.