This is an example of a prototype, black anodized aluminum part with o-ring sealing surfaces on both ends.
You can detect a very poorly sealed surface yourself by simply feeling it with your fingers. Make sure your hand (and the metal) is clean and dry, then press your fingers against the surface. A poorly sealed coating will feel sticky. A well sealed coating will be smooth and slick. Keep in mind that this test will not determine if a seal is satisfactory – only if it is unsatisfactory.
Another quick and easy seal test is to mark the coated surface with a "Marks-a-Lot," permanent black, felt tip marker. If the surface is well sealed it should not absorb the ink. After a minute or two, try removing the mark with a cloth dampened with acetone (acetone-water nail polish remover will do). If the mark is not completely removed by the damp cloth the seal is considered questionable at best.
Coating density is important because it is an indicator of the integrity of the anodic coating. It can give you some assurance that the anodizer is furnishing a hard, abrasion resistant coating. Ford Motor Co. requires a coating density of 12 milligrams per square inch on 0.3 mil coatings used on the exterior of its automobiles.
If you want ADT and/or coating density data specific to your job, be sure to tell the anodizer ahead of time. These are destructive tests and the anodizer will have to attach test coupons to the racks carrying your work.