Some pigments like viridian and alizarin crimson are transparent and therefore great for glazing. They are different in staining qualities, that viridian it is non-staining and can be removed easily from the surface; with alizarin crimson will leave a stain.

Colors can vary in transparency, like cerulean blue, oxide of chromium and Naples yellow, these are naturally opaque and although the manufacturers try to by pass this with glycerin you should use these colors carefully, you can loose the translucency of the watercolor you have laid down because of this.

Watercolor is available in many forms, dry cakes, tubes and bottles of concentrated color. The dry cakes are very concentrated with less glycerin, and it takes more effort with your brush to raise the color. Put water onto the cake and let it sit before starting, it will soften it.

Tubes and bottles contain more glycerin and are soft. They are useful in larger scale paintings and when mixing quantity. It is so much easier to squeeze out some color and add water to it than from a cake. The bottle colors are very vivid and used in illustrations.

Plastic palettes with deep wells are ideal for mixing large washes. You can use ceramic dishes as well. The palettes usually come in a line up of five squares in white so you can see the colors you choose.