@punkarsenic asked how to create a 'fountain pen' effect digitally here
I spent an hour or so figuring out how to do this; if you want a legitimate method support this artist and pay the $5.50 for their much more legit inking brushes
Here's what mine look like:
Start with a new layer
Go to Layer Properties (if you don't see, go to Window >> Layer Property)
Select Border Effect and change to Border of Watercolor
You'll want to adjust 'Area' and 'Blurring width' (i left it alone for now)
Right click on your levels window to create a new Correction layer, Levels Correction
You're gonna want to adjust this depending on your preference. Here are my settings for the image above (the grey arrow was moved closer to the white arrow to get sharper lines)
And then you get that cool 'ink running together' effect
Now the downsides are obviously that a) it's not transparent and b) its a lot of trial and error.
To get around the transparency problem, you can color over the lineart with Multiply and Overlay modes:
or you can combine the correction layer, lineart, and a layer filled with white (from top to bottom in that order) and 'Convert brightness to opacity' to color underneath.
Hope this helps!