Etching cream is not recommended for large surface areas because of its potentially toxic fumes. Acid washing is another method of etching glass, but it is best left to professionals due to the potentially toxic nature of the ingredients used in the process. Sandblasting, etching and acid washing are all permanent and cannot be reversed

Summary:
Remove window glass from frame, wash and allow to dry. Rent a sandblaster and buy sand/grit from the rental store. Protect the work area with heavy canvas drop cloths and don protective eye goggles, work gloves and face mask. Place window glass in center of drop cloth and follow manufacturer's directions carefully to etch the entire surface of the glass. Clean window glass of excess grit, and replace glass in window frame.