What to Know Before You Buy Watercolor Supplies
You don't need a lot of supplies to get started painting with watercolor. You will need a basic set of good-quality watercolor paints, a range of papers of different textures and weights (so you can test for yourself how each one works), and a few brushes. Just add some water to thin them for painting, and a palette to mix your colors on, and you are all ready to begin. It's that easy. If you want to experiment more with different techniques, you might also like to try out some mediums.
Watercolor Paints
Paints come in tubes or pans (small blocks). Pans are cheaper, easily accessible, but tend to dry out. Pans are ideal for small areas of color and watercolor sketching. Paint in tubes has to be squeezed onto a palette; it's easier to use for large areas of color. There's a big difference between student and professional paints; professional paints have more pigment in them in proportion to extender and filler and may be more lightfast. You don't need a lot of colors to create a good painting so it is better to buy a few quality paints than many cheap colors. For the price, though, some student-grade watercolors are useful and have worthwhile qualities, and some artists use them quite successfully.
Watercolor Paper
Watercolor papers come in three surfaces: rough, which has a textured surface; hot-pressed or HP, which has a fine-grained, smooth surface; and cold-pressed (or NOT), which has a slightly textured surface and is the paper used most often by watercolor artists. The thickness of the paper is indicated by its weight; paper less than 356 gsm (260 lb) should be stretched before use.
Sable brushes are considered the ultimate in watercolor brushes because of the fine point the hairs reach, their ability to spring back into shape, and the amount of paint they hold. Less expensive options are brushes with a mixture of sable and synthetic hairs or 100% synthetic brushes. Unlike choosing paint, start with the cheaper brushes and upgrade as you become more proficient. But if you can afford medium-priced brushes or one or two higher priced brushes, they are well worth it. You don't want brushes that are so cheap that the hairs fall out or splay easily. That will be frustrating and you won't be able to achieve the painting effects you desire.
Watercolor Mediums
Mediums are added to watercolor to create special effects. Aquapasto (Buy from Amazon) is a gel medium which thickens washes and provides texture. Gum arabic (Buy from Amazon) increases paint transparency and gloss. Ox gall (Buy from Amazon?) improves the flow of washes over hard papers. Masking fluid blocks out sections of a painting while you paint further - it's removed by rubbing it off the paper when the paint is dry. Iridescent medium adds a sparkle. Granulation Medium produces grainy colors rather than smooth.