Using acrylic paints for calligraphy needs the paint to have a suitable runny texture, but it also should have a stable and long-lasting durability over time. This can be acheived two ways, either by using premixed artist quality acrylic paints or if you are adventurous you can mix your own using pigments. (As for me i would rather use the premixed paints).
Selecting the paint
There are many varieties of acrylic paint available which range from house paints to artist quality and then there are pigment powders, so depending on your experience with mixing pigments it might be a better idea to make your ink from artist quality paint tubes.
Paint thinning mediums are a clear acrylic that is used to thin the paint without changing the pigment or texture, there are a range of surface finishes available (from matte to high-gloss). So it is necessary to use some medium when you make your calligraphy ink in order to maintain the purity of the paint and to ensure it does not become overly diluted. Basically pick what kind of finish you want for your ink (matte or glossy). Then purchase the medium of choice.
Making the Ink
The use of distilled water is recommended for mixing with your medium to give the finished ink a good texture, The ideal base mixture of water to medium is 50/50 (The quantity depends on how much ink you want to produce). without diluting it to much.
After preparing your medium and water mixture, start adding small amounts of the artist paint and stir till you have a smooth texture, continue adding small amounts of paint up to a total of 50 percent of the water/medium mixture, stirring till you have a smooth mixture with a texture of thin cream.
Chemical inclusions in the paint
The pH of your ink mixture (no less than 8) is important, if the pH falls below this, it will acquire a thick cheese-like texture which will make it no good as an ink. You can check the inks pH by using litmus paper or by smell (the ink should have a slight ammonia smell) If there is no smell of ammonia just add a few drops of ammonia to return to the correct pH level.
Another thing you should be aware of is ‘foaming” since paints have a surfactant added, mixing it with a water/medium mixture could start it to foam, but by the addition of a few drops of a defoaming agent will prevent this from occurring (follow the manufacturers directions on the label).
When you are happy with your ink it is time to put it in a container, just remember to make sure the container has an air tight cover to prevent the water content evaporating.