-- water solubility, so I can create wash sketches using them.
-- portability, so I can use them in my fountain pens or otherwise easily carry them around.
Most fountain pen inks suit me just fine, since they are dye-based inks, which are not waterproof (or lightfast) for the most part. They are water-soluble.
"Pigmented" inks would be more permanent (more waterproof and more lightfast), but it's hard to make a suspension that will work in fountain pens without clogging them.
Hence, my sketches are neither "waterproof" nor "lightfast". My sketches are for me, not for posterity. It's the process that engages me. Not the product. I'm more interested in a little fun!
✱ My technique is to make my initial sketch with a pen and then come back in with a waterbrush (loaded with clear water) or a regular watercolor brush and wash/blur the lines. I try to use the wash to indicate form and volume and shadow areas.
The corkscrew on the right is an example of an ink sketch done with a wash. Another example of an ink+wash sketch is here.
Excellent Introduction to the technique : Beyond the Pen: Fountain Pen Ink as Watercolor Wash, by Jamie Williams Grossman
-- Waterproof, Permanent, Bulletproof, Archival, Eternal, Pigmented Inks: What do they mean?, from FPN
-- Direct Sketching with Pen and Ink: Just Jump into the Deep End of the Swimming Pool, from Roz Wound Up (whom I venerate)
-- About ink, and a thank you, by Nina Johansson
-- Richard Binder's undated: Inks: The Good, the Bad, and the Ugly
-- Calligraphers and Pen+Ink Sketchers share ink selection criteria. Here is a good intro to calligraphy inks: Selecting Calligraphy Inks: Tests and Reviews
So now to it---> My current FAVORITE sketching inks:
☛ Private Reserve Velvet Black
☛ the ink in the disposable black Pilot Razor Point Pen
☛ Private Reserve Chocolat
☛ Iroshizuku Yama-guri
☛ Iroshizuku Kiri-same
-- Ink wash - color tests
-- More fountain pen and wash
-- Ink and wash tool recommendations?
-- Ink Samples and Setting Up Lightfastness Tests
-- Ink Samples with Wash - Brown Inks
-- Pen Maintenance, by John Mottishaw
-- Best Pen For Artists, thread, with links, in the Fountain Pen Network
-- Glossary of Pen Terms, from Richard Binder
Choose your INK-->
For endless ink reviews--> Of hundreds of inks (in hundreds of colors) made for fountain pens, see the Index of Ink Reviews in the Fountain Pen Network forum.
-- The Writing Desk: Brown
-- The Swab Shop: Brown Inks
The problem with both of these site, for MY purposes, is that neither show me how the inks wash. But that's okay because once I pick out some likely-looking colors, now I can . . .
Order sample vials--> of each color that piques my interest:
-- Goulet Pen: Ink Samples
-- Pear Tree Pen: Fountain Pen Ink Samples
OR! Join the Ink Drop at Goulet Pen and "for only $10 per month . . . you'll receive 5 fountain pen ink samples" each month, selected by Brian and Rachel Goulet.
✱ Remember: "waterproof" is not the same thing as "lightfast".
Waterproof--> If you are interested in waterproof ink AND portability for fountain pens --- that is, so-called "waterproof inks" that won't damage your fountain pen -- here is a thread entitled Complete List of Waterproof Inks, in the Fountain Pen Network forum. (Though started in '06, that thread's most recent posting was less than a year ago, so it's fairly up-to-date.)
Waterproof inks, once dry, will stay put under later watercolor washes. Explore the coloring book technique!
Lightfast--> A lightfast+waterproof ink that is portable for fountain pens is Platinum Carbon Ink. One portable (non-dip) pen that is built to use it: the Platinum Carbon Pen. (And here is the cleaning kit for pens using these pigmented inks.)
Also rumored to be water-soluble AND lightfast, is the pigmented Higgins Fountain Pen India Ink.
✱ More on the relative lightfastness of inks for fountain pens:
☛ Jamie Grossman's extensive lightfastness tests are here.
☛ Fading/lightfastness-test -- Graphic results, from the Fountain Pen Network.
☛ Ink Sample Fading Test -- Also from the Fountain Pen Network.
☛ Noodler's Ink Properties table PDF
Another option for those yearning for lightfastness is to use "acrylic inks" in a fountain pen. Risky business! Here is a thread, Adapting Acrylic Inks for FP Use, that offers some guidance.
✱ Of course: Neither "waterproof" nor "lightfast" inks will wash well. They will smear when wet, but not wash well.
✱ Comments, please! Let me know your thoughts. Please also post links to new informative and useful web pages about sketching inks. Thank you!
Illustration above by Zach Johnsen. I call it 'Smiling Ink Heads'