In addition to Bida, at about 100 years ago, hot-glass was worked at Oyo (and another near-by location—the name of which escapes me at the moment, in Nupe territory). These are the ONLY places in West Africa where glass was hot-worked, as is routine in most other places of glass production.

Nigerian powderglass is or was more local to Ile-Ife, which is Yoruba country. The industry there seems to have declined in the 1960s. However, I hope that at the Conference in Istanbul, later this year, we may get some new information. If not then, I am in contact with scholars who are investigating this industry—so we'll know eventually.

Yes, scarification, as practiced in Nigeria, often does include short parallel lines, similar to the bead patterns.

Jamey