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Domain structures were observed in polycrystalline, high permeability grain oriented 3-percent Si-Fe before and after formation of a forsterite coating. A 200 kV scanning electron microscope was used for domain observations. Significant alterations in the supplementary (flux closure) domain structure and a substantial refinement in the 180° domain wall spacing were produced by the forsterite coaling. Increased pinning of 180° walls by inclusions was observed after fotsterite coating. These inclusions are most likely parlicles of forsterite lying just below the sheet surface. The effects of forsterite coatings on domain structure are believed to be caused by changes in surface roughness occurring after forsterite coating. Possible effects of these variations in domain structure on losses are discussed.