This tip only applies when painting on surfaces that are gessoed.
It seems natural to use water to create thin, transparent layers of color while painting with acrylics, especially when creating an underpainting. Unfortunately, adding too much water will break down the acrylic binder that holds the pigment together. What this means is that, over time, the paint will detach (or flake off) from the surface. The general rule is to use a maximum of 30% water to 70% paint. To create thin layers, I use an acrylic airbrush medium instead. This gives me the transparency I would normally get with water without weakening the paint. Additionally, the airbrush medium’s viscosity is similar to that of water, making wash effects easier.
In the example above, I used thin washes on the table, background as well as the egg.