collection HELM&HELM sammlung 0700GOOGLE1st HOME&ABROAD

https://web.archive.org/web/20210812013123/https://sites.google.com/site/sturgardde/ polygraficum/polygraphicum bloGspOt 3749 https://0700polygraf.blogspot.com/2021/05/httpweb.html dweed 2073 https://twitter.com/PeterHelm12/status/1770567047866446122

https://www.royalacademy.org.uk/art-artists/book/monuments-des-arts-du-dessin-chez-les-peuples-tant-anciens-que-modernes