This is a dip pen with an adjustable line width. It has become popular for apply masking fluid for watercolors.
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PDF) Dependence studies of new compounds in the rhesus monkey, rat and mouse (1986)
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Pacific Arc Ruling Pens – K. A. Artist Shop
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Pacific Arc Ruling Pens – K. A. Artist Shop
2017 ACVIM Forum Research Abstract Program - Abstract - Europe PMC
trello: April 2015