A relevant patent on cathode island formation

By Carl E. Atkins
Patent US2850674


https://patentimages.storage.googleapis.com/00/16/d5/e1462b599958b0/US2850674.pdf


See also:
http://www.rfcafe.com/references/radio-news/low-plate-potential-tubes-january-1957-radio-television-news.htm