Chalk will wash away with the rain, to protect the sidewalk.
A concrete sidewalk is a giant outdoor canvas for a street artist. With just a box of pastel chalks, a cloth, water, can of hairspray and a range of techniques --- an artist can make impressive temporary masterpieces to share freely with the passing spectators on the sidewalk gallery.
Preparation
The first stage of creating a chalk picture on the sidewalk is to draw a white outline of the image to be filled in with colored chalk pastels. Street artists often copy from a picture of an existing work such as from the great masters -- from Michelangelo to Pablo Picasso; or the work may be an original illustration. She may rule out a square grid on the printed picture reference and then increase the grid size on the pavement to keep the dimensions of the image in proportion to the printed copy.
Shading
A street artist needs to work quickly for he is always at the mercy of the weather conditions. The technique of shading is used to fill in areas of the chalk picture with color and shade. He will use the side of the chalk to shade quickly across his selected area. The more pressure he applies to the chalk, the darker the shade will be. Conversely, with less pressure applied to the chalk, he creates lighter graduated tones.
Blending
Another important art chalk technique is to blend colors together to create smoother color transitions. The artist will shade an area with one color, then introduce a second color chalk pastel into the mix. Hence, she shades over the first color with the second and blends the two colors together with the help of blending sticks, tissues or an old cloth.
Wet Effect
Chalk pastels are dipped into a container of water for up to 6 minutes, until the tip of the chalk pastel is soaked and softened. Then, the chalk can be applied to the sidewalk like paint. In this technique, the colors will be easier to blend together and also will be able to cover large areas of the concrete canvas.
