Cola pens

I first heard of "cola pens" in Denise Lach's book Calligraphy, which isn't about writing text so much as drawing with letters (and other marks) -

"It is not difficult," she writes, "to cut into an aluminium can with scissors, so you can easily make nibs of various shapes yourself. The cut-out piece of metal is then folded to create a reservoir which - when open - allows the ink to flow through. The sharp edges of the folded metal can be smoothed with emery cloth or crocus paper. You can write with the cola pen in any direction: it lends itself well to pushing as well as dragging."

I made some pens (various videos and instructions can be found online) and had a play.

For some reason one pen makes a little click  when used in certain positions, and a spurt of ink results ... which might be unwanted, but could be useful -

This one, with the square tip, can be held upright and twirled to make perfectly circular marks -

Next time there's an empty "cola" can around the house, I shall make some more of these playthings...