I use acrylic inks a lot. GhoulFriday asked that I write a post about them so here it is.
Here are some examples of some things I have painted using acrylic inks.
Compared to acrylic paints inks are a really different beast, They are much thinner and have very little body to them. What this means is that you can achieve very cool effects with them. I use a lot of textiles and airdry clays in my work and and I frequently use techniques that add even more texture to them, if I were to use a heavily bodied paint the paint would fill the subtle textures I have created.
I have used 2 brands of acrylic inks:
Liquitex : These inks have super-fine fine pigments in them, I never thin them when using them. You can get both opaque and transparent colors.
FW Inks: These inks seem to have a larger pigment size than the Liquitex inks. I use them as well, but only for certain effects. When thinning them use alcohol, 95% pure or better, in a ratio of 1 part ink to maybe 10 parts alcohol or more depending on what you are doing.
Application: I primarily use an airbrush when applying inks, sometimes at 15-20 PSI, mostly at 5-7 PSI. For some effects though I do use a brush, I put the ink in a paper cup and add alcohol and brush it on. Because the inks are so thin, they dry extremely fast, especially if you have thinned with alcohol. Also since they are alcohol activated if you do not seal between layers of inks you can actually erode previous layers of inks of you are not careful, this can be a curse or a blessing depending on how you look at it, I never seal between layers. Because they dry so fast it also means you can keep painting, and I am an impatient artist.