Check your paint – your coloring agent – to ensure that it is acrylic, or water-based. Do not mix an oil-based paint with an acrylic gel medium.
Eyeball the acrylic gel medium and the paint to make sure you have enough to create a 4-to-1 ratio.
Pour 4 parts of the acrylic gel medium to a plastic bowl. Use an old spoon or an old measuring spoon. The tool itself doesn’t matter; using the same tool for the gel medium and the paint does. Using the same tool ensures your measurements will be the same for each medium.
Add 1 part acrylic paint to the plastic bowl. Try to find one with a lid so you can store any leftover paint.
Stir the two elements together with a craft stick until they are thoroughly blended.
Test the mixture on a piece of poster board to ensure it is the consistency you wish. If it is too thick – and sometimes it is – place one drop of water at a time in the mixture and stir it thoroughly. Then do another test. Resist the urge to add more than one drop of water at a time.
Store any remaining paint in a cool, dry place.