i have used Speedball India ink for practice work many, many times - no thinning/solvent needed. have also used the Speedball acrylic color inks, again, no thinning/solvents. altho they do tend to cause a little more tip dry than the regular black india ink
air pressure needs to be turned down some due to the very thin consistency, and it does tend to "spider" when trying to get really fine lines, but other than that, i like it - very easy to use/spray
cleanup is accomplished quite easily with Fantastic spray cleaner mixed 50/50 with water.
give it try, you may like it.
