Remove the lids and place them top down on your workbench in front of each color. Use a small brush to pick up powder from the jar, then pat the brush on the lid. Apply the color to the desired area of the model. Then brush out and blend the color with a large soft brush. White is used to provide a highlighted base-coat for subsequent colors and really brings out details.
Grimy colors work well to tone down and blend underlying colors.
Apply as much or as little color as you want. If you apply too much, simply wash the powders off with a little soapy water, let dry, and reapply. Doc O'Brien's Weathering Powders can also be used as weathering washes by mixing them with water or thinners. Be sure that the thinner you select is compatible with the surfaces you are weathering and experiment on a scrap piece before applying to your model. We have found that models made of wood stand up very well to handling without too much of the powder rubbing off.