. . "While any surface-active paper penetrant can be employed, these compounds are know to be especially useful: ethyleneglycol monobutyl ether, ethyleneglycol phenyl ether, diethyleneglycol monobutyl ether, triethyleneglycol monobutyl ether, diethyleneglycol monopropyl ether, dipropyleneglycol monopropyl ether, propyleneglycol monopropyl ether, propylene glycol monobutyl ether, 1,2-butanediol, 1,2 pen" . .