Mix the DI water, in a beaker, with the commercial sealing additive, in the proportions suggested by the additive manufacturer. Use a pH meter to make sure that the pH is between 5.5 and 6; if not, add either acetic acid or ammonia until a reliable pH meter reads the proper pH.
Place the beaker on the heating plate. Heat the solution of DI water and additive until the solution boils.
Place the anodized aluminum into the sealing bath. For each micrometer of the thickness of the anodized coating, leave the aluminum in the bath for 2 minutes.
Turn off the heat. Using heat-resistant gloves, pour off the contents of the beaker into a waste receptacle. Run cold DI water over the anodized aluminum, and then remove it from the beaker.