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a. Start with a File 6 x 2 in with 72 dpi
b. Make a new Layer by hitting the New Layer Button
c. Name the layer Base by double clicking on it.
d. Hit D to reset your colors to Black and White.
e. Go to Filter>Render>Clouds
f. Go to Image>Adjustments>Brightness/Contrast...
and adjust it to these settings:
Contrast: -45