Wide‐line nmr measurements show that anodic coatings formed in 15% and 12 A/ft2 for 1 hr and sealed for 30 min in boiling water at pH 6 contain groups plus 1–4% physically adsorbed water. Nitrogen adsorption measurements show a surface area of about 20 m2/g for unsealed coatings and about 5 m2/g for sealed coatings. The unsealed coatings contain about pores/cm2 of mean radius of 60Aå. About 46% of the water contained in a sealed coating is on a surface. From this, and from nmr line widths, a surface area of 260 m2/g is estimated. The difference between the gas adsorption and nmr estimates of surface areas is explained by the model proposed for the coating structure, one consisting of an array of microcrystallites estimated to be about 25Å in radius. Gas adsorption analyzes only the major pore surfaces, but nmr analyzes the crystallite surfaces as well. Sealing is regarded to be primarily a surface reaction on the crystallites.