Coating fluid applicable by hand for sol-gel film formation

A coating solution for obtaining sol-gel films, said coating solution being that the coating solution has a solid matter and a solvent, wherein:

• the solid matter has a silicon oxide oligomer obtained by subjecting an alkoxysilane to hydrolysis and polycondensation in an acid aqueous solution,
• the solvent has an organic solvent having a boiling point of 100° C. or higher and a viscosity of 3.5 mPa·s or lower and the acid aqueous solution,
• the number average molecular weight of the silicon oxide oligomer in terms of polystyrene is 500-4000,
• the content of the solid matter in the coating solution is 8-30 weight %,
• the content of the silicon oxide oligomer in the solid matter is 10 weight % or greater,
• the alkoxysilane comprises trialkoxysilane and tetraalkoxysilane, and
• the weight ratio of a silicon oxide oligomer derived from the trialkoxysilane to a silicon oxide oligomer derived from the tetraalkoxysilane is 20:80 to 50:50.