You have your colors squeezed out into your palette and you've tossed away the tubes. Now you need to know which watercolors are opaque and which colors are transparent. Remember mixing opaques with too many colors ends up in mud. What do you do?
Create an Opaque Test Chart
• Using waterproof black India Ink, paint a straight line about a 1/4 inch wide onto a piece of watercolor paper. If you have a lot of colors or several palettes, paint several lines. Allow to dry completely.
• Swash each color from your palette across the black line.
• Allow to dry.
• Label each color for future reference.
If the color covers the black line, it is an opaque color.
If the black line shows through, it is a transparent color.
Make sure you have a good mix of paint to water. If you have more water than paint you will end up with a confusing test result like my gamboge and cadmium green in the lower right side of the picture. I created my charts on 300 lb. watercolor paper and then used a three hole punch on one side of the chart and keep them stored in a three ring binder with other test charts. Label the charts with the colors and brands of paint is also very helpful.