Birchwood Casey (Gel)The Birchwood Gels make it easier to achieve an even patina and work well on vertical surfaces. One gallon of a Birchwood Gel Patina generally covers 200 sq. ft. per coat. They are available in 8oz., 32oz., 1 gallon, and 5 gallon sizes. The Birchwood Gel Patinas are not concentrated and are ready to use. Gel solutions for Bronze, Brass, and Copper: Antique Black Gel (M 24). Antique Brown Gel (M 38). Gel solution for Iron and Steel: Presto Black Gel