I’m learning that there are many different approaches to Dorodango, but for me, it all comes down to extracting the purest clay possible by using water.
Take a 5 gallon bucket, fill half with dirt, the rest with water. Stir until fully mixed. Wait 20 minutes and pour water through a fine filter like a paint cloth. Let the water sit for about 12 hours. Pour off the water and what is left is clay. Spread it out, let it dry, crush it fine, sift it, and voila!
The traditional approach as seen in Gardner’s book is to start with dirt, sift it through various sizes of strainers, keeping separate grades of dirt from normal to fine to clay. Throughout the process one pours dirt over the slowly drying ball of mud. For me, I have found that the clay I am able to get from the my dirt is so good that I have even bypassed the adding of additional dirt. I start with very fine clay and just enough water to moisten the clay so that it is not sticky but not lumpy. Then I let it dry, looking in on it frequently so that I can ensure as round a ball as possible. In the end, the goal is to have a round, hardened mudball that can be shined until you can see your reflection.