My favorite pouring mediums are (these are all Golden products) Clear Tar Gel, Self-Leveling Gel, and GAC800. The Clear Tar Gel and Self-Leveling Gel both need about 20-40% water added if you are pouring in a dry warm climate – like out here in New Mexico. You don’t need to add water in wet cool climates.
Adding water will enable a thinner layer to be applied. If you apply it too thickly, the top part of the layer will dry first, then the rest of the acrylic will dry slower and shrink down in volume, creating crevises or cracking on the top. Its better to pour a few thin layers, one on top of the other after they dry, then one thick layer that may crack.
GAC800 does not need any water added, as it is made especially for pouring, and can be poured very thickly without crevising or cracking. The GAC800 is the easiest to pour, but has a slight yellow or cloudy look to it, that is more noticeable the thicker the pour. I like to use this in thick layers to simulate a wax or encaustic look.
When I pour, I pour very gently, from a low height and a soft angle. If you pour from a high height, or vigorously, the medium may jolt out of the container creating bubbles. A light spray of alcohol on the surface before pouring, or even after pouring while the medium is still wet will eliminate bubbles too.
More pouring articles:
For more information on pouring, check out Nancy Reyner’s book Acrylic Illuminations.