I also added lighter highlights and details to the building. The blemishes in the sky were covered with a new semi-opaque wash, adding a small amount of titanium white to increase opacity. After blemishes are covered, a transparent glaze, using matte medium, water, and pigment is applied to the sky. Other glazes were applied to subdue inappropriate lights and to adjust the temperature of selected areas . Transparent glazing at this point tends to unify transparent and opaque passages by giving a transparent look to areas that are actually opaque.
Art is no exception, so experiment with acrylics.
You might just fall in love with this versatile medium.