which pens?

GT076 - FILM OPAQUER PEN – THIN POINT
http://www.bonwyke.co.uk/products/tools.asp#
Film Opaquer Pens
http://www.ramasa.co.uk/productframes/ancilliaryspares/misc1/startopaque.htm

Kimoto Pake Pen

http://www.intaglioprintmaker.com/shop/default.asp?c1=0&c2=2