Fregert S, Gruvberger B
Contact Dermatitis. 1984 Sep;11(3):141-3. doi: 10.1111/j.1600-0536.1984.tb00958.x.
Colophony (rosin) has been fractionated into 2 parts, an acidic and a neutral fraction. Routine patch testing with neutral components gives positive reactions at a 40% higher frequency than routine patch testing with colophony (20%) (w/w in pet.). A concentration of 60% colophony is suggested for routine patch testing.