Decarburized grain oriented silicon steel is provided with an annealing
separator which forms a glass film after the final high temperature
anneal. The magnesia used as the annealing separator has a total chlorine
level of 0.01 to 0.20% by weight based on the weight of magnesia with at
least 0.01% metal chloride selected from the group of Mg, Ca, Na and K.
The chloride addition acts to seal the coating surface during the final
anneal to control diffusion and stabilize the secondary grain growth. The
glass film which forms during the anneal may be laser scribed for domain
refinement without coating damage. The magnesia may also contain additions
of phosphates, TiO.sub.2, SiO.sub.2, Cr and B. The temperature of the
magnesia is maintained below 25.degree. C. to control hydration and
eliminate the need for other additives in the magnesia slurry to control
hydration.
