Wash all of the gravel thoroughly in a bucket of water to remove any bits of leaves or sticks. Swirl the bucket to mix the gravel thoroughly and wash off loose soil and dirt.
Run the cleaned gravel through a set of graduated metal sieves to separate the material into particles of similar size. Separate the material held on each sieve into individual piles. You can sort through the largest pieces by hand.
Pour a pile from a fine sieve into a gold pan and add water. Swirl the pan continuously to separate the grains by density, pouring off the lighter material as you swirl. This action concentrates dense rock and mineral grains, including any diamonds that may be present, at the bottom of the pan.
Coat a flat or slightly concave surface with a layer of grease such as paraffin, beeswax, petroleum jelly or some mixture. Position the surface so that it is slightly tilted.
Pour concentrated ore from the pan onto the high edge of the greased surface and wash the grains gently with a stream of water. Diamonds will stick to the grease while other rock and mineral grains will wash away. Remove any grains sticking to the grease by hand and set them aside. Run the concentrate across the greased surface a second time.
Repeat the concentration and grease separation processes with the contents of the remaining sieves. Inspect the reserved grains, if any, by hand to determine whether they are diamonds.