Scenic Designer and Professor Ming Cho Lee is renown for, amongst other things, carrying a roll of onion skin tracing paper with him during critiques. Rather than deface a student’s work, he would lay the tracing paper down, and draw on the paper. Thus the nickname.
Of course, when working with pencil on paper, Ming Wrap, is a wonderful, inexpensive way to layer developmental drawings. Of course, there’s an app for that. Morpholio has created Trace because, well, pixels are even cheaper than cheap tracing paper. Working alone, or on top of files, images, or photos, race (especially with a stylus) replicates working with layers of tracing paper for sketching, and/or design development.
Of course, much easier to share than a diazo print, and without the toxic ammonia fumes.