A method for forming a protective layer for a dielectric material in an alternating
current type plasma display is provided. In this connection, a coating sol solution
is provided which can form a protective layer on a large area substrate without
the need to introduce any expensive equipment, the protective layer thus formed
being excellent in properties such as strength, adhesion, transparency, and protective
properties and capable of being formed by a sol-gel process without use of the
conventional vacuum process. The sol solution comprises a dispersion of a precursor
to magnesium oxide in a specific form. A method for film formation, using this
solution is also provided.
