To color with colored pencils like a professional we need to be able to blend well. Blending is not to be confused with mixing. See the link at the bottom of this page for tips on how to mix colors using colored pencil. Coloured pencil can only be mixed by layering one colour over another. Blending smooths out this layering and softens or smudges the harsh edges, but it does not mix colours or get rid of scribbly lines. There are several methods of blending coloured pencil, all of them aim to make your colored pencil work look smooth and no one way is best. Fabulous artists use lots of different methods and get stunning results. Try them all, the only method that requires any real expense is number 4, so you may as well experiment and see which you prefer.
1. Blend simply by lightly layering one colour over another. Beautiful results can be obtained with a light hand and tiny pencil strokes. All this method involves is patience. This is probably the only real 'rule' as such with colored pencil and it applies to everything you do, except for the final layers. (See the link at the bottom on how to burnish). If you apply color with too much pressure it makes it difficult to add more color, so always with colored pencil work lightly.
2. Use a blending stump or tortillon. This are really, really inexpensive to buy, so it is certainly worth trying this method and seeing if you like it. This won't really blend two colours together, but will smudge and smooth out the color where the edges meet. I don't ever use this method mainly because it seems to flatten out the tooth of the paper making it difficult to apply more colours. I think really these are better for burnishing than they are for blending.
3. Use a light coloured pencil (which you probably already have anyway) or a special colourless blending pencil. These are very inexpensive again, so it is worth buying one and trying it. Go over the entire area you wish to blend with the pencil. A white or light coloured pencil will lighten what is underneath it. Some colourless blenders may darken the work underneath. Be aware that some blenders will add a layer to your work that may make it difficult to add more colour on top. To add further colour you may have to use a fixative spray. I personally don't like the waxy layer a lot of the colorless blenders seem to add, as again it makes it difficult to add more layers over the top.
4. My preferred method. I use odourless mineral spirits to blend my colours. I use a cheap, synthetic bristle brush to apply it. This pushes the pigment into the grain of the paper. I don't like to see little flecks of paper showing through my work and this method seems to smooth out the layers of color really well. You will read on the net that a lot of people suggest using baby oil to do this. I haven't tried this. I wouldn't want to try it either. I want my work to have as long a life span as possible. I would doubt that baby oil is archival, although even if it were, I don't think I would want to cover my paper with oil. Some people don't like to use mineral spirits for various health reasons, I have seen products like Zest It, recommended as a natural alternative. I haven't tried these and again I want to be sure my work ages well.
Try these methods out and before long you will be using colored pencils like a pro!